fix(ci): backport release-v1 CI fixes

[MilesCranmerBot]

This bundles the low-risk CI-related backports from recent master PRs that still make sense on release-v1:

• raise the Python floor from 3.8 to 3.9 in package metadata / conda env
• replace the remaining Python 3.8 CI leg with 3.9
• pin the conda-forge workflow away from generic 3 to avoid free-threaded Python resolution
• make backend update PR branches version-specific

I kept this intentionally narrow rather than backporting unrelated workflow churn.

[MilesCranmer]

@MilesCranmerBot could you also make it so that all the CI runs on PRs to the release-v1 branch? Right now only a single check gets launched.

[MilesCranmerBot]

Done in 9cdeb39. I added release-v1 to the PR triggers for Linux, Windows, macOS, Docker, Apptainer, and CodeQL, so PRs targeting release-v1 should now launch the full CI set instead of just the single branch-push check.

I didn’t run the test suite locally since this is a workflow-trigger-only change.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (release-v1@6e645a0). Learn more about missing BASE report.

Additional details and impacted files

@@              Coverage Diff              @@
##             release-v1    #1164   +/-   ##
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  Coverage              ?   93.24%           
=============================================
  Files                 ?       21           
  Lines                 ?     1555           
  Branches              ?        0           
=============================================
  Hits                  ?     1450           
  Misses                ?      105           
  Partials              ?        0           

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[MilesCranmer]

@MilesCranmerBot some of the CI is still failing; could you look for other fixes that need to be in place using the other PRs?

[MilesCranmerBot]

Found the missing backport and pushed it in 3cad894.

The remaining failing job was Check types (3.10, ubuntu-latest), and the culprit was a typing fix from master that had not been brought over: fix: typing issue in export format (2b173ff on master).

I backported the corresponding pysr/export.py change so the JAX/Torch export columns are assigned via pd.Series(..., index=output.index), which fixes the mypy error on release-v1.

Quick local check run:

• python -m mypy --ignore-missing-imports pysr ✅

PR: #1164
Commit: 3cad894