Update tests for removal of python36 from Github Actions hostedtoolcache

[stuhood]

Github Actions recently removed python3.6 from /opt/hostedtoolcache, which means that our pantsbuild/actions/expose-pythons action does not expose it.

This causes tests which require Python 3.6 to fail (example) on main (and in branches).

[kaos]

Would be nice with a comment somewhere (next to the resource target in the BUILD file perhaps) mentioning how to generate these platform json files.. ;)

[WorkerPants]

I tried to automatically cherry-pick this change back to each relevant milestone, so that it is available in those older releases of Pants.

❌ 2.16.x

I was unable to cherry-pick this PR to 2.16.x, likely due to merge-conflicts.

Steps to Cherry-Pick locally

To resolve:

1. (Ensure your git working directory is clean)
2. Run the following script to reproduce the merge-conflicts:

   git fetch https://github.com/pantsbuild/pants main \
     && git fetch https://github.com/pantsbuild/pants 2.16.x \
     && git checkout -b cherry-pick-19901-to-2.16.x FETCH_HEAD \
     && git cherry-pick 1bb84ed4720525b79fcdf3fd3664b8c087043982

3. Fix the merge conflicts and commit the changes
4. Run build-support/cherry_pick/make_pr.sh "19901" "2.16.x"

Please note that I cannot re-run CI if a job fails. Please work with your PR approver(s) to re-run CI if necessary.

✔️ 2.17.x

Successfully opened #19905.

✔️ 2.18.x

Successfully opened #19904.

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When you're done manually cherry-picking, please remove the needs-cherrypick label on this PR.

Thanks again for your contributions!

🤖 Beep Boop here's my run link