Redmine

This patch enables GitHub Actions to run on stable branches, executing builds for testing and linting.

While GitHub Actions are currently executed for the master branch, they are not yet enabled for stable branches. In particular, running a complete build, including rubocop and stylelint, for the latest stable branch (6.0-stable) should help prevent mistakes like those in #42088 and contribute to the overall quality of Redmine.

This patch ensures that necessary builds are executed and succeed for the 6.0, 5.1, and 5.0 stable branches.

• Add GitHub Actions workflows for linting and testing
• Backport necessary fixes from trunk to ensure linting and testing succeed

The details of the builds for each branch are as follows:

The patches are separated by branch:

• Patches for the 6.0-stable branch: 000x-6.0-stable-*.patch
• Patches for the 5.1-stable branch: 000x-5.1-stable-*.patch
• Patches for the 5.0-stable branch: 000x-5.0-stable-*.patch