Pass GITHUB_ACTIONS from host when building and testing linux wheels

[thabbott]

Run times for the release workflow have increased significantly since v0.51.2: compare https://github.com/contrailcirrus/pycontrails/actions/runs/9563516040 (1 hour, limited by linux wheels) to https://github.com/contrailcirrus/pycontrails/actions/runs/9411025885 (20 minutes, limited by windows wheels).

This is because the GITHUB_ACTIONS environment variable, which is used to selectively skip tests in test_leo.py that download large imagery files, is not passed from the host to the container used to build and test wheels on linux.

This PR ensures that the GITHUB_ACTIONS environment variable is correctly set when building and testing wheels on all hosts. (See https://cibuildwheel.pypa.io/en/stable/options/#environment-pass.)

Release workflow runtime with this change is similar to v0.51.2: https://github.com/contrailcirrus/pycontrails/actions/runs/9568292058/job/26378142375.

Changes

Internals

• Ensure GITHUB_ACTIONS environment variable is available when building and testing wheels on linux.

Tests

• [x] QC test passes locally (make test)
• [ ] CI tests pass

Reviewer

@mlshapiro