3.12.0 release

[nkoenig]

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

🎈 Release

Preparation for 3.12.0 release.

Comparison to 3.11.2: ignition-gui3_3.11.2...ign-gui3

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 #508 (01cd472) into ign-gui3 (ab48b05) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           ign-gui3     #508   +/-   ##
=========================================
  Coverage     73.82%   73.82%           
=========================================
  Files            30       30           
  Lines          3270     3270           
=========================================
  Hits           2414     2414           
  Misses          856      856           

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