PR Summary

I only updated .mailmap to removed duplicate emails, since generate_credits.py complained about them. There may still be duplicate entries for people who changed or use multiple email addresses.

Waiting on #17491.

PR Checklist

• [N/A] Has Pytest style unit tests
• [N/A] Code is Flake 8 compliant
• [N/A] New features are documented, with examples if plot related
• [a] Documentation is sphinx and numpydoc compliant
• [N/A] Added an entry to doc/users/next_whats_new/ if major new feature (follow instructions in README.rst there)
• [N/A] Documented in doc/api/api_changes.rst if API changed in a backward-incompatible way