Generate a list of changed files when a new version is tagged

[desrosj]

The HelpHub includes a section for listing all files changed during a release. Generating this list of files is usually done by manually running an SVN or Git command.

svn diff --summarize https://core.svn.wordpress.org/tags/6.1.1 https://core.svn.wordpress.org/branches/6.2 | grep '^M'

As an example, this gives a list of files modified from 6.1.1 to 6.2. I don’t have the equivalent command handy, but this can also easily be accomplished using Git.

Generating a list of files requires a level of technical knowledge (checking out a repository, running a CLI command), but it shouldn’t.

When a new version is tagged, a GotHub Action should run and generate the list of files so that any contributor can use the list to update documentation in the HelpHub, or wherever else it’s needed.

[ridesirat]

This is a must.
Even for security reasons.
Some security plugins send a log of changed files. Sometimes is useful to confirm it's a Core change and not a malicious one.

[wildworks]

This issue appears to be an improvement to the development flow itself, and not a required task for the 6.9 release. I will change the milestone to 7.0, but please let me know if I missed anything.

[desrosj]

I've not had the time to work on this during the 7.0 cycle.

Fixes: #640003

Generating a list of files changed between two WordPress releases currently requires technical knowledge — checking out a repository and running a manual SVN or Git command such as:

svn diff --summarize https://core.svn.wordpress.org/tags/6.1.1 \
    https://core.svn.wordpress.org/branches/6.2 | grep '^M'

This PR adds .github/workflows/generate-changed-files.yml, a GitHub Action that generates this list automatically, making it accessible to any contributor without requiring a local environment.

## How it works

Automatic — triggers on any version tag push (e.g. 6.6.2). The previous release tag is detected automatically using
git tag --sort=-version:refname, so pushing 6.6.2 compares
6.6.1 → 6.6.2 with no manual input required. Major releases (e.g.
7.0) correctly resolve to the last patch of the previous series
(e.g. 6.9.4), not the .0 tag.

Manual (workflow_dispatch) — contributors can trigger the workflow from the Actions tab at any time, providing two tag inputs to compare any two releases. Useful for back-filling documentation.

## Output

• Step Summary — a Markdown-formatted list visible directly on the Actions run page. No download or technical setup required.
• Workflow Artifact — a downloadable changed-files-<tag>.txt file for use in tooling or copy-pasting into documentation.

## Test plan

• [ ] After merging to trunk, navigate to Actions → Generate Changed Files List → Run workflow, provide two existing tags (e.g. compare_tag: 6.6.1, base_tag: 6.6.0), and confirm the step summary shows the correct list of changed files.
• [ ] Push a new version tag and confirm the workflow triggers automatically, resolves the correct previous tag, and produces the expected output.