GitHub Actions updates and improvements for 7.0

[desrosj]

This ticket is for various updates and improvements for Core's GitHub Actions workflows.

Previously:

• 6.9 (#63170)
• 6.8 (#62221)
• 6.7 (#61564)
• 6.6 (#60733)
• 6.5 (#59805)
• 6.4 (#58867)
• 6.3 (#57865)
• 6.2 (#57572)

This new post-branching task is meant for any tasks that should be run immediately after creating a new numbered branch. Currently, this only consists of GitHub Actions-related tasks.

In addition to the pre-existing replace:workflow-references-local-to-remote task, a new clean:workflows task is being added that deletes the workflow files that are only intended for trunk.

Trac ticket: Core-64227

Waiting to merge this until the discussions on #10512 are resolved to ensure this task deletes all of the correct files.

[desrosj]

In 61286:

Build/Test Tools: Introduce post-branching Grunt task.

In [59673], a Grunt subtask was introduced to convert workflow file references in GitHub Action workflows from local ones to remote ones that target the trunk branch.

The workflow-references-local-to-remote Grunt task should be run after creating a new numbered branch to take advantage of the work started in [58165].

This commit introduces a new target for the clean Grunt task: workflows. Running grunt clean:workflows will delete all workflow files that are not intended to exist outside of trunk.

Another Grunt task (post-branching) has also been added as a way to group all tasks taht should run within a newly created branch. For now, this contains clean:workflows and replace:workflow-references-local-to-remote. But more can be added in the future as more aspects of the branching process are automated.

Props johnbillion.
See #64227.

Fixed in r61286.