Otherwise the example is invalid because the matplotlibrc parser
doesn't understand multi-line commands. See #9184.

This is a temporary fix, the true fix is to fix the parser (again, see #9184).

I thought about adding a test but couldn't figure out the best way to do so given the comment structure of the file: uncommenting all lines won't work, uncommenting the specific line of axes.prop_cycle is brittle, uncommenting only lines that start with an rcParams key will break when we do add multi-line support. Suggestions welcome, but otherwise, this can always be merged while keeping #9184 open.

• 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