Since we bumped the min numpy version to 1.10, numpy scalars are now
also instances of numbers.Number.

Closes#7795.

(Related note: we can't do the same with iterable/isinstance(..., Iterable) as documented athttps://docs.python.org/3/library/collections.abc.html#collections.abc.Iterable.)

PR Summary

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