Use GZ_PI instead of M_PI to fix windows builds

[azeey]

🦟 Bug fix

Fixes #2229

Summary

Some of the M_PI usage was introduced in #2185, but I also found another in the marker example.

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 #2230 (b32b980) into gz-sim7 (45233fc) will decrease coverage by 0.01%.
The diff coverage is n/a.

❗ Current head b32b980 differs from pull request most recent head 5e66988. Consider uploading reports for the commit 5e66988 to get more accurate results

@@             Coverage Diff             @@
##           gz-sim7    #2230      +/-   ##
===========================================
- Coverage    64.75%   64.75%   -0.01%     
===========================================
  Files          357      357              
  Lines        29145    29144       -1     
===========================================
- Hits         18874    18872       -2     
- Misses       10271    10272       +1     

see 2 files with indirect coverage changes

[azeey]

I think the windows failure is unrelated, so I'll go ahead and merge this.