ci: run slow tests separately

[atravitz]

we only run slow tests when code is pushed to main, but it's not clear from our current test set up that that is a difference between PR CI and scheduled or manual CI.

Checklist

• All new code is appropriately documented (user-facing code must have complete docstrings).
• Added a news entry, or the changes are not user-facing.
• Ran pre-commit: you can run pre-commit locally or comment on this PR with pre-commit.ci autofix.

Manual Tests: these are slow so don't need to be run every commit, only before merging and when relevant changes are made (generally at reviewer-discretion).

• GPU integration tests
• example notebook testing
• packaging tests: run this for any large feature PRs or PRs that add test data.

Developers certificate of origin

• I certify that this contribution is covered by the MIT License here and the Developer Certificate of Origin at https://developercertificate.org/.

[github-actions]

🚨 API breaking changes detected! 🚨
View logs for this step

[atravitz]

@mikemhenry- this might cause issues with our codecov. thoughts?

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.01%. Comparing base (f7561cd) to head (eb24b73).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1827      +/-   ##
==========================================
- Coverage   95.27%   93.01%   -2.27%     
==========================================
  Files         201      201              
  Lines       17589    17575      -14     
==========================================
- Hits        16758    16347     -411     
- Misses        831     1228     +397     

Flag	Coverage Δ
fast-tests	93.01% <ø> (?)
slow-tests	?

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