SNOW-1705656: Lists in mixins get applied twice

[sfc-gh-fcampbell]

SnowCLI version

main

Python version

Python 3.12.3

Platform

macOS-14.6.1-arm64-arm-64bit

What happened

Using mixins that contain lists of dicts, like artifacts, the list is applied twice. In this minimal example

definition_version: 2
entities:
  pkg:
    type: application package
    manifest: app/manifest.yml
    meta:
      use_mixins:
        - artifacts_mixin
mixins:
  artifacts_mixin:
    artifacts:
      - src: app/*
        dest: ./

The resultant project model is (irrelevant fields omitted)

definition_version: '2'
entities:
  pkg:
    type: application package
    artifacts:
    - src: app/*
      dest: ./
      processors: []
    - src: app/*
      dest: ./
      processors: []
    manifest: app/manifest.yml

I believe this is because _unique_extend doesn't properly exclude list items that are dicts when defaults have been added, since the items are no longer identical:

Console output

No response

How to reproduce

Evaluate the above snowflake.yml file in a debugger to see that the list is duplicated