Disable distortion camera test on Linux

[scpeters]

🦟 Bug fix

Part of #2243.

Summary

Disable the distortion camera test on Linux for gz-sim8, since it has been failing there. It works on gz-sim7 on Linux. It is already disabled on macOS and doesn't run on windows, so just disable it outright on gz-sim8.

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

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (b991a99) 65.66% compared to head (f2762c1) 65.62%.
Report is 6 commits behind head on gz-sim8.

❗ Current head f2762c1 differs from pull request most recent head fa952bc. Consider uploading reports for the commit fa952bc to get more accurate results

Files	Patch %	Lines
src/systems/tracked_vehicle/TrackedVehicle.cc	75.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           gz-sim8    #2247      +/-   ##
===========================================
- Coverage    65.66%   65.62%   -0.05%     
===========================================
  Files          324      324              
  Lines        30944    30918      -26     
===========================================
- Hits         20319    20289      -30     
- Misses       10625    10629       +4     

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