[Backport stable-f44] fix(release): tag selection in changelogs.py

[aurora-backport]

This is an automated backport of PR #2363 to stable-f44.

Please review the changes.

Original PR Description:

This PR fixes an issue with choosing incorrect tags when we have multiple builds on the same day. We now group tags by date and make sure to only select the same date when there are multiple builds.

Tested:

$ python -m doctest .github/changelogs.py -v
Trying:
    imgs = lambda tags: {"aurora": {"RepoTags": tags}}
Expecting nothing
ok
Trying:
    get_tags("stable", imgs(["stable-20260602.1", "stable-20260609", "stable-20260609.1"]))
Expecting:
    ('stable-20260602.1', 'stable-20260609.1')
ok
Trying:
    get_tags("stable", imgs(["stable-20260602.1", "stable-20260609.1", "stable-20260609.2"]))
Expecting:
    ('stable-20260602.1', 'stable-20260609.2')
ok
Trying:
    get_tags("stable", imgs(["stable-20260526", "stable-20260602", "stable-20260602.1", "stable-20260609", "stable-20260609.1"]))
Expecting:
    ('stable-20260602.1', 'stable-20260609.1')
ok
14 items had no tests:
    changelogs
    changelogs.START_PATTERN
    changelogs.calculate_changes
    changelogs.generate_changelog
    changelogs.get_commits
    changelogs.get_image_digest
    changelogs.get_images
    changelogs.get_manifests
    changelogs.get_package_groups
    changelogs.get_packages
    changelogs.get_sbom
    changelogs.get_versions
    changelogs.main
    changelogs.parse_sbom_packages
1 item passed all tests:
   4 tests in changelogs.get_tags
4 tests in 15 items.
4 passed.
Test passed.

Closes #2362.

Disclaimer: written with iteration from Sonnet 4.6. Test plan is mine.

[codacy-production]

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