Improve markup in `enum.rst`

[ezio-melotti]

Documentation

For example in https://docs.python.org/3/library/enum.html#enum.IntFlag there are several names that use italic (*...*) instead of the correct role (:class:, :func:, etc.). There might be more throughout the page.

Linked PRs

• gh-110679: Improved markup in enum.rst #110747