ign -> gz Tick-tock Python Libs : gz-math

[methylDragon]

Part of overarching: gazebo-tooling/release-tools#698
Follow-up to: gazebo-tooling/release-tools#765

In gazebo-tooling/release-tools#765, gz-math Python bindings were tick-tocked to allow use of ignition and gz. But the symlinks that are being created on the debbuilder are malformed, even though local builds work fine...

This PR fixes that by abusing relative links (it breaks on absolute links for some reason.)

Compare the built .deb from this

• broken: https://build.osrfoundation.org/job/ign-math7-debbuilder/741/
  • (the symlink points to one layer too shallow) (../../../../usr/lib/XXX, when it should be ../../../../../usr/lib/XXX)
• fixed: https://build.osrfoundation.org/job/ign-math7-debbuilder/745/
  • (symlink now points to ../gz/XXX)

Test downstream build using fixed debbuild:
Build is unstable because of deprecation warnings, not test failures, which this fixes!

[codecov]

Codecov Report

Merging #466 (8496dbe) into main (49eba8f) will not change coverage.
The diff coverage is n/a.

❗ Current head 8496dbe differs from pull request most recent head 2c20008. Consider uploading reports for the commit 2c20008 to get more accurate results

@@           Coverage Diff           @@
##             main     #466   +/-   ##
=======================================
  Coverage   99.69%   99.69%           
=======================================
  Files          74       74           
  Lines        6845     6845           
=======================================
  Hits         6824     6824           
  Misses         21       21           

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[methylDragon]

Build is unstable because of deprecation warnings, not test failures, which this fixes!