Blast545/fix unused gcc warnings

[Blast545]

🦟 Bug fix

Fixes gcc warnings appearing in CI:
https://build.osrfoundation.org/job/gz_sim-ci-main-jammy-amd64/66/gcc/

Summary

Does not change at all the tests, just voids the variables so the compiler takes them as read and won't emit the warning

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

All modified and coverable lines are covered by tests ✅

Project coverage is 65.91%. Comparing base (cffd297) to head (e986c4b).

Additional details and impacted files

@@           Coverage Diff            @@
##           gz-sim8    #2388   +/-   ##
========================================
  Coverage    65.91%   65.91%           
========================================
  Files          327      327           
  Lines        31314    31314           
========================================
  Hits         20641    20641           
  Misses       10673    10673           

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[Blast545]

🧑‍🌾 Green CI, except on windows, INTEGRATION_mesh_inertia_calculation.test_ran seems to be flaky. FYI @Crola1702

Merging!