Fix: System testing on DO took too many resources

[hoh]

Problem: Running system testing on DigitalOcean for every push consumed a lot of resources and failed frequently.

We now start to have integration testing using pytest, which provides a better confidence that things actually work.

Solution: Only test on DO open Pull Requests and not every push. In the future, consider only running when merged on main.

[github-actions]

The PR is focusing on updating a GitHub Actions workflow file. This change is small and simple, likely due to a change in the rules for the workflow, or updating the workflow to a new version. The diff shows that the workflow is being updated and not removed or renamed, which is a common practice in GitHub Actions. The workflow is still being run and tested, which is good.

The changes do not seem to affect the core functionality of the system, or the overall architecture of the codebase, so the risk of introducing bugs is low. The impact on the codebase and review process is also minimal.

diff --git a/.github/workflows/test-on-droplets-matrix.yml b/.github/workflows/test-on-droplets-matrix.yml
index c67c1688..84746938 100644
--- a/.github/workflows/test-on-droplets-matrix.yml
+++ b/.github/workflows/test-on-droplets-matrix.yml
@@ -1,107 +1,30 @@
-name: "Test on DigitalOcean Droplets"
-
+# These are end-to-end tests running on ephemeral DigitalOcean "Droplet" virtual machines
+# with the different operating systems that are supported.
+#
+# The main focus of these tests is to ensure that the packaging works on all supported platforms
+# and to ensure the compatibility of dependencies (system and vendored) across these platforms.
+name: "Testing on DigitalOcean Droplets"
+
+# Run automatically on main branches, Pull Request updates and allow manual execution using `workflow_dispatch`.
 on:
-  push
+  push:
+    branches:
+       - main
+  pull_request:
+    types:
+       - 

RED: 
The PR is updating the GitHub Actions workflow file, but it is significant in terms of the number of jobs and steps involved. This change is likely to be used for running more comprehensive tests, or for setting up a new CI/CD pipeline.

The diff shows that the workflow is being updated to include new jobs and steps, which could potentially affect the system's functionality. The risk of introducing bugs is moderate, but the impact on the codebase and review process is high. The PR will require a deep understanding of the project's architecture and its current CI/CD pipeline.

```diff
diff --git a/.github/workflows/test-on-droplets-matrix.yml b/.github/workflows/test-on-droplets-matrix.yml
index c67c1688..84746938 100644
--- a/.github/workflows/test-on-droplets-matrix.yml
+++ b/.github/workflows/test-on-droplets-matrix.yml
@@ -1,107 +1,30 @@
-name: "Test on DigitalOcean Droplets"
-
+# These are end-to-end tests running on ephemeral DigitalOcean "Droplet" virtual machines
+# with the different operating systems that are supported.
+#
+# The main focus of these tests is to ensure that the packaging works on all supported platforms
+# and to ensure the compatibility of dependencies (system and vendored) across these platforms.
+name: "Testing on DigitalOcean Droplets"
+
+# Run automatically on main branches, Pull Request updates and allow manual execution using `workflow_dispatch`.
 on:
-  push
+  push:
+    branches:
+       - main
+  pull_request:
+    types:
+       - 

BLACK: 
The PR is updating the GitHub Actions workflow file to a significant extent. The diff shows a large number of new jobs and steps, and the update is likely to affect the entire CI/CD pipeline.

The risk of introducing bugs is high, as the changes will require a deep understanding of the project's architecture and its current CI/CD pipeline. Only experienced developers should review this PR, as it involves a significant change to the project's CI/CD pipeline.

```diff
diff --git a/.github/workflows/test-on-droplets-matrix.yml b/.github/workflows/test-on-droplets-matrix.yml
index c67c1688..84746938 100644
--- a/.github/workflows/test-on-droplets-matrix.yml
+++ b/.github/workflows/test-on-droplets-matrix.yml
@@ -1,107 +1,30 @@
-name: "Test on DigitalOcean Droplets"
-
+# These are end-to-end tests running on ephemeral DigitalOcean "Droplet" virtual machines
+# with the different operating systems that are supported.
+#
+# The main focus of these tests is to ensure that the packaging works on all supported platforms
+# and to ensure the compatibility of dependencies (system and vendored) across these platforms.
+name: "Testing on DigitalOcean Droplets"
+
+# Run automatically on main branches, Pull Request updates and allow manual execution using `workflow_dispatch`.
 on:
-  push
+  push:
+    branches:
+       - main
+  pull_request:
+    types:
+       - 

Please note that the categorization is based on the provided information and may not be 100% accurate. It's always recommended to review the PR in a safe environment before deciding on the complexity level.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 43.87%. Comparing base (8318c43) to head (0350344).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #614   +/-   ##
=======================================
  Coverage   43.87%   43.87%           
=======================================
  Files          55       55           
  Lines        4978     4978           
  Branches      587      587           
=======================================
  Hits         2184     2184           
  Misses       2677     2677           
  Partials      117      117           

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[MHHukiewitz]

LGTM, simple restructuring