chore(ci): Split pre-release tests into cron job

[effigies]

This splits pre-release tests into a cron job instead of on every PR/commit. It hasn't happened lately on this repository, but these tests are distracting for PRs that are unrelated.

This sets up the ci/prerelease branch to allow triggering these tests intentionally during a PR (such as this one).

@Remi-Gau If you wouldn't mind having a quick look, I would appreciate it.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.41%. Comparing base (7e0e509) to head (04fbb10).
⚠️ Report is 7 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1466      +/-   ##
==========================================
- Coverage   95.42%   95.41%   -0.01%     
==========================================
  Files         209      209              
  Lines       29822    29822              
  Branches     4483     4483              
==========================================
- Hits        28457    28455       -2     
- Misses        930      931       +1     
- Partials      435      436       +1     

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[Remi-Gau]

Writing down what was talked about in person.

Scheduled workflow only notify some maintainers so may be good to open an issue when the workflow fails (we do that on nilearn).

See https://docs.github.com/en/actions/concepts/workflows-and-actions/notifications-for-workflow-runs

Notifications for scheduled workflows are sent to the user who initially created the workflow.
If a different user updates the cron syntax, in the schedule event in the workflow file, subsequent notifications will be sent to that user instead.
If a scheduled workflow is disabled and then re-enabled, notifications will be sent to the user who re-enabled the workflow rather than the user who last modified the cron syntax.

[effigies]

Adding some notes for from nilearn for reference:

• [MAINT] improve workflow to test on nightly dependencies nilearn/nilearn#4364
• https://github.com/nilearn/nilearn/blob/abbbe55/.github/workflows/nightly_dependencies.yml

@Remi-Gau I plan to understand what you did and include it here, but if you get inspired and I haven't gotten around to it, feel free to push to this branch.

[Remi-Gau]

feel free to push to this branch.

Done

[effigies]

Thanks!