Update to the latest release of the CloudEvents SDK - 2.1

[n3wscott]

Changes

We have released a new version of the CloudEvents SDK for Go, there are a few bug fixes and testing features you might want. See the release notes: https:/cloudevents/sdk-go/releases/tag/v2.1.0

Submitter Checklist

These are the criteria that every PR should meet, please check them off as you
review them:

• Includes tests (if functionality changed/added)
• Includes docs (if user facing)
• Commit messages follow commit message best practices
• Release notes block has been filled in or deleted (only if no user facing changes)

See the contribution guide for more details.

Double check this list of stuff that's easy to miss:

• If you are adding a new binary/image to the cmd dir, please update
  the release Task to build and release this image.

Reviewer Notes

If API changes are included, additive changes must be approved by at least two OWNERS and backwards incompatible changes must be approved by more than 50% of the OWNERS, and they must first be added in a backwards compatible way.

[tekton-robot]

This PR cannot be merged: expecting exactly one kind/ label

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[tekton-robot]

This PR cannot be merged: expecting exactly one kind/ label

Available kind/ labels are:

kind/question: Issues or PRs that are questions around the project or a particular feature
kind/bug: Categorizes issue or PR as related to a bug.
kind/flake: Categorizes issue or PR as related to a flakey test
kind/cleanup: Categorizes issue or PR as related to cleaning up code, process, or technical debt.
kind/design: Categorizes issue or PR as related to design.
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kind/feature: Categorizes issue or PR as related to a new feature.
kind/misc: Categorizes issue or PR as a miscellaneuous one.

[n3wscott]

/label kind/cleanup

[n3wscott]

/kind cleanup

[vdemeester]

/lgtm
/cc @afrittoli

[afrittoli]

Thank you!
/approve

[tekton-robot]

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