prepare 12.3.0

[nkoenig]

Signed-off-by: Nate Koenig [email protected]

🎈 Release

Preparation for 12.3.0 release.

Comparison to 12.2.0: sdformat12_12.2.0...sdf12

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 ignition-release (as needed):

Note to maintainers: Remember to use Squash-Merge

[codecov-commenter]

Codecov Report

Merging #766 (43db9a4) into sdf12 (8707d41) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##            sdf12     #766   +/-   ##
=======================================
  Coverage   89.23%   89.23%           
=======================================
  Files          76       76           
  Lines       12081    12081           
=======================================
  Hits        10781    10781           
  Misses       1300     1300           

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