6.8.0 release

[nkoenig]

🎈 Release

Preparation for 6.8.0 release.

Comparison to 6.8.0: https://github.com/gazebosim/gz-gui/compare/ignition-gui6_6.7.0...ign-gui6

Needed by https://github.com/gazebosim/gz-sim/pull/1989

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[bot]]

Codecov Report

Merging #539 (c6ad0b3) into ign-gui6 (bd683eb) will increase coverage by 0.03%. The diff coverage is n/a.

@@             Coverage Diff              @@
##           ign-gui6     #539      +/-   ##
============================================
+ Coverage     69.81%   69.85%   +0.03%     
============================================
  Files            40       40              
  Lines          5324     5324              
============================================
+ Hits           3717     3719       +2     
+ Misses         1607     1605       -2     

see 1 file with indirect coverage changes