warnings.catch_warnings docstring: obsolete compat note

[jwilk]

The docstring for warnings.catch_warnings.__init__ reads:

For compatibility with Python 3.0, please consider all arguments to be
keyword-only.

This makes little sense these days.

Linked PRs

• gh-129842: Remove obsolete requirement reference #129845

[sobolevn]

Please, feel free to send a PR with the fix. It is a good first issue :)