Extends github-actions updater to support wider CalVer format

[lorengordon]

Fixes #14677

What are you trying to accomplish?

Currently Dependabot only recognizes refs as versions that prepend a 'v' or that use periods as separators. However, neither is required for CalVer formats. This PR updates the parser to allow CalVer formats of the form YYYYMMDD as recognized versions.

Checklist

• I have run the complete test suite to ensure all tests and linters pass.
• I have thoroughly tested my code changes to ensure they work as expected, including adding additional tests for new functionality.
• I have written clear and descriptive commit messages.
• I have provided a detailed description of the changes in the pull request, including the problem it addresses, how it fixes the problem, and any relevant details about the implementation.
• I have ensured that the code is well-documented and easy to understand.

[Copilot]

Pull request overview

This PR updates Dependabot’s git ref/version detection so GitHub Actions (and other git-based dependencies using GitCommitChecker) can treat compact CalVer tags like YYYYMMDD (e.g., 20260408) as version refs, enabling update detection for actions pinned to that format.

Changes:

• Extend Dependabot::GitCommitChecker::VERSION_REGEX to match 8-digit compact CalVer tags.
• Add specs verifying pinned_ref_looks_like_version? recognizes compact CalVer refs.
• Add specs ensuring latest-version selection respects “precision” and does not mix compact CalVer with dotted CalVer tags.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
common/lib/dependabot/git_commit_checker.rb	Adds an 8-digit alternative to the version-matching regex so compact CalVer tags are treated as versions.
common/spec/dependabot/git_commit_checker_spec.rb	Adds coverage for compact CalVer pins and ensures version selection stays within the same precision/format.

[lorengordon]

Thank you @thavaahariharangit !