Prepare for 9.9.1 Release

[scpeters]

🎈 Release

Preparation for 9.9.1 release.

Comparison to 9.9.0: sdformat9_9.9.0...sdf9

Needed by <PR(s)>

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 #1197 (87dca08) into sdf9 (7d312cb) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             sdf9    #1197   +/-   ##
=======================================
  Coverage   88.33%   88.33%           
=======================================
  Files          63       63           
  Lines       10075    10075           
=======================================
  Hits         8900     8900           
  Misses       1175     1175           

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.