compat: state in the module docstring that it also contains utilities

Maybe it's not ideal but that's the current reality, and I wouldn't like
to break tradition by renaming the file.

Author: bluetech

src/_pytest/compat.py

@@ -1,5 +1,5 @@
 # mypy: allow-untyped-defs
-"""Python version compatibility code."""
+"""Python version compatibility code and random general utilities."""
 
 from __future__ import annotations