Fix warnings on Jammy

[chapulina]

🦟 Bug fix

• Backport Add .cc extension to suppress CMake warnings #428

Summary

We also support Fortress on Jammy, and these have been showing up.

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.

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[codecov]

Codecov Report

Merging #464 (093690b) into ign-gui6 (c9b9fc0) will increase coverage by 0.03%.
The diff coverage is n/a.

❗ Current head 093690b differs from pull request most recent head 0887125. Consider uploading reports for the commit 0887125 to get more accurate results

@@             Coverage Diff              @@
##           ign-gui6     #464      +/-   ##
============================================
+ Coverage     67.97%   68.00%   +0.03%     
============================================
  Files            39       39              
  Lines          5239     5239              
============================================
+ Hits           3561     3563       +2     
+ Misses         1678     1676       -2     

Impacted Files	Coverage Δ
src/plugins/scene3d/Scene3D.cc	49.87% <0.00%> (+0.25%)	⬆️

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