Restore GUI support for macOS

[srmainwaring]

🦟 Bug fix

Fixes #1812

Summary

Restore the change to src/cmd/cmdsim.rb.in from #1225 that allows macOS to run the GUI.

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

[codecov]

Codecov Report

Merging #1813 (3db57c9) into gz-sim7 (bb85aa2) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           gz-sim7    #1813   +/-   ##
========================================
  Coverage    64.42%   64.42%           
========================================
  Files          341      341           
  Lines        27151    27151           
========================================
  Hits         17492    17492           
  Misses        9659     9659           

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