Changelog: update for release of v 1.2.3

[jrfnl]

Includes:

• Mention of all relevant changes.
• Adding a link for the version diff.
• Updating the VERSION document with the version nr for the release.

Note: the Markdown check will fail the build on an unavailable link - this is the comparison link between this and the previous version, which isn't available yet, as the tag will only be created after this PR has been merged.
In other words: this is fine and as expected.

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Release checklist

General

• Verify, and if necessary, update the allowed version ranges for various dependencies in the composer.json - no PR needed
• Add changelog for the release - this PR
  ✏️ Remember to add a release link at the bottom!
• Update the version number in the VERSION file - this PR

Release

• Merge this PR
• Make sure all CI builds are green.
• Tag and create a release against the stable branch (careful, GH defaults to develop!) & copy & paste the changelog to it.
  ✏️ Check if anything from the link collection at the bottom of the changelog needs to be copied in!
• Make sure all CI builds are green.
• Close the milestone
• Open a new milestone for the next release
• If any open PRs/issues which were milestoned for this release did not make it into the release, update their milestone.
• Fast-forward develop to be equal to stable

Publicize

• Toot about the release.
• Tweet about the release.

[jrfnl]

Social media release notifications:

• https://phpc.social/@phpcs/114670038614839907
• https://x.com/PHP_CodeSniffer/status/1933116793788170628