PR Summary

At some point, one of our dependencies must have required pytz, but then recently dropped it. Pandas also requires it, but because we install the nightly wheels using --index-url, pip can only install files from that index, which does not contain pytz. And we want to use that index exclusively because we only want the nightly wheels, and nothing else. So explicitly install pytz when running nightlies.

Also, make -i into the more explicit --index-url, and word-wrap that step.

Fixes #25431

PR Checklist

Documentation and Tests

• [n/a] Has pytest style unit tests (and pytest passes)
• [n/a] Documentation is sphinx and numpydoc compliant (the docs should build without error).
• [n/a] New plotting related features are documented with examples.

Release Notes

• [n/a] New features are marked with a .. versionadded:: directive in the docstring and documented in doc/users/next_whats_new/
• [n/a] API changes are marked with a .. versionchanged:: directive in the docstring and documented in doc/api/next_api_changes/
• [n/a] Release notes conform with instructions in next_whats_new/README.rst or next_api_changes/README.rst