Prepend to PYTHONPATH in tests

[scpeters]

🦟 Bug fix

Fixes failing python tests

Summary

Preserve the existing PYTHONPATH by prepending instead of replacing. This is needed since we started using a virtual environment in CI.

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)
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[scpeters]

I think both e527979 and gazebo-tooling/release-tools#1203 are needed to fix the python system loader integration test

[scpeters]

I think both e527979 and gazebo-tooling/release-tools#1203 are needed to fix the python system loader integration test

I'm going to temporarily reconfigure the homebrew jenkins job to use the release-tools branch from gazebo-tooling/release-tools#1203

[scpeters]

@osrf-jenkins run tests please

[scpeters]

I think both e527979 and gazebo-tooling/release-tools#1203 are needed to fix the python system loader integration test

I'm going to temporarily reconfigure the homebrew jenkins job to use the release-tools branch from gazebo-tooling/release-tools#1203

https://build.osrfoundation.org/job/gz_sim-ci-pr_any-homebrew-amd64/1074/

[scpeters]

https://github.com/Mergifyio backport gz-sim8

[mergify]

backport gz-sim8

✅ Backports have been created

• #2681 Prepend to PYTHONPATH in tests (backport #2673) has been created for branch gz-sim8