Prepare for 12.7.1 release

[iche033]

🎈 Release

Preparation for 12.7.1 release.

Comparison to 12.7.0: sdformat12_12.7.0...prep_12.7.1

Needed by gazebosim/gz-sensors#327

Checklist

• Asked team if this is a good time for a release
• There are no changes to be ported from the previous major version
• No PRs targeted at this major version are close to getting in
• Bumped minor for new features, patch for bug fixes
• Updated changelog
• Updated migration guide (as needed)
• Link to PR updating dependency versions in appropriate repository in gazebo-release (as needed):

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[codecov]

Codecov Report

Merging #1243 (e7f7e60) into sdf12 (f23fac7) will not change coverage.
The diff coverage is n/a.

❗ Current head e7f7e60 differs from pull request most recent head 0dc3abd. Consider uploading reports for the commit 0dc3abd to get more accurate results

@@           Coverage Diff           @@
##            sdf12    #1243   +/-   ##
=======================================
  Coverage   92.03%   92.03%           
=======================================
  Files          79       79           
  Lines       13090    13090           
=======================================
  Hits        12047    12047           
  Misses       1043     1043           

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