PR Summary

Using (n, 3) as marker style to specify a circle marker is deprecated. Use
"o" instead.

Using ([(x0, y0), (x1, y1), ...], 0) as marker style to specify a custom
marker path is deprecated. Use [(x0, y0), (x1, y1), ...] instead.

PR Checklist

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