Branching tasks for 7.1

[wildworks]

This ticket is for tracking the tasks required after branching as ​documented in the handbook.

On w.org:

• Update WP_CORE_DEV_BRANCH.

In trunk:

• Update SECURITY.md to include the new branch.
• Update the GitHub actions workflows that test branches to include the new branch.
• Update the .version-support-(mysql|php).json files in trunk.

In the new branch:

• Run npm run grunt post-branching to update GitHub Actions workflow files.
• Pin the LOCAL_PHP and LOCAL_DB_VERSION values to the highest supported versions.

On Trac:

• Create new tickets for the next release.

Previously:

• 7.0: #64966
• 6.9: #64235
• 6.8: #63164

This includes all the changes required post-branching for trunk:

• Bump the version in version.php, composer.json, package.json, and package-lock.json to 7.2-alpha.
• Add 7.1.x to the list of versions receiving security updates in SECURITY.md.
• Add the 7.1 branch to the test-old-branches.yml workflow matrices, and update CURRENTLY_SUPPORTED_BRANCH.
• Add 7.1-RC2 to the upgrade testing workflow matrices. Since these workflows test tagged versions available through WP-CLI, the pre-release version needs to be used until 7.1 is released.
• Add 7-2 keys to .version-support-mysql.json and .version-support-php.json.

Note: the SVN revision in version.php (7.2-alpha-63162-src) is a placeholder and will need to match the actual revision at commit time.

## Use of AI Tools

AI assistance: Yes
Tool(s): Claude Code
Model(s): Claude Opus 5
Used for: Applying the mechanical post-branching version/matrix updates following the handbook and the previous 7.0 branching PR (#11376); reviewed and verified by me.

Trac ticket: https://core.trac.wordpress.org/ticket/65844

## Use of AI Tools