Prepare for 7.3.1 release

[iche033]

🎈 Release

Preparation for 7.3.1 release.

Comparison to 7.3.0: gz-rendering7_7.3.0...prep_7.3.1

Needed by gazebosim/gz-sim#1960

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 #843 (db5bcd9) into gz-rendering7 (563cbbf) will not change coverage.
The diff coverage is n/a.

@@              Coverage Diff               @@
##           gz-rendering7     #843   +/-   ##
==============================================
  Coverage          77.37%   77.37%           
==============================================
  Files                164      164           
  Lines              14459    14459           
==============================================
  Hits               11187    11187           
  Misses              3272     3272           

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