Disable deprecation messages about onFoo connections

[azeey]

🦟 Bug fix

Summary

Alternative to #493. See https://github.com/gazebosim/gz-gui/pull/493/files#r982750363

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

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 #534 (d67d86a) into gz-gui7 (bf42b84) will increase coverage by 0.06%.
The diff coverage is 91.66%.

❗ Current head d67d86a differs from pull request most recent head fee57e2. Consider uploading reports for the commit fee57e2 to get more accurate results

@@             Coverage Diff             @@
##           gz-gui7     #534      +/-   ##
===========================================
+ Coverage    69.13%   69.19%   +0.06%     
===========================================
  Files           44       44              
  Lines         4921     4938      +17     
===========================================
+ Hits          3402     3417      +15     
- Misses        1519     1521       +2     

Impacted Files	Coverage Δ
src/plugins/world_stats/WorldStats.cc	94.11% <91.30%> (-0.89%)	⬇️
src/Application.cc	85.97% <100.00%> (+0.03%)	⬆️

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[jennuine]

Thanks for the fix!