fix(codepipeline-actions): default branch for CodeCommit is master (under feature flag)

[daschaa]

Closes #27710.

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[aws-cdk-automation]

The pull request linter has failed. See the aws-cdk-automation comment below for failure reasons. If you believe this pull request should receive an exemption, please comment and provide a justification.

A comment requesting an exemption should contain the text Exemption Request. Additionally, if clarification is needed add Clarification Request to a comment.

[daschaa]

Exemption Request: I ran the integration tests and the snapshots have been changed. So I think a new integration test is not needed.

[kylelaker]

I am not sure but wouldn't this probably need a feature flag? Since a user may have deployed when the default was master and built their stack when that was the expectation (according to https://docs.aws.amazon.com/codecommit/latest/userguide/history.html, any stacks built prior to March 2021 or repositories created via the console/API prior to Jan 2021), I think updating this to main would require them to make a code change in order to continue having a functioning stack.

[daschaa]

@kylelaker Thanks for the feedback. :) I think you are right - it would make sense to introduce a feature flag here. I'll try to implement this.
And if one of the maintainers says that it doesn't need a feature flag after all, I can revert the changes.

✅ Updated pull request passes all PRLinter validations. Dismissing previous PRLinter review.

[mikewrighton]

Will approve once the build is fixed.

[mergify]

Thank you for contributing! Your pull request will be updated from main and then merged automatically (do not update manually, and be sure to allow changes to be pushed to your fork).

[aws-cdk-automation]

AWS CodeBuild CI Report

• CodeBuild project: AutoBuildv2Project1C6BFA3F-wQm2hXv2jqQv
• Commit ID: f0344bb
• Result: SUCCEEDED
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[mergify]

Thank you for contributing! Your pull request will be updated from main and then merged automatically (do not update manually, and be sure to allow changes to be pushed to your fork).