[RaphaelFakhri]

check-peps.py splits Python-Version into a comma-separated list, but _validate_python_version() ends with return when a version has no micro part. The first two-segment version (for example 3.12) stops the generator, so later versions in the list are never checked.

For example, these headers pass the linter today:

Python-Version: 3.12, 4.0
Python-Version: 3.x, 3.01
Python-Version: 2.7, 3.0.a

This change replaces the return with continue, so each version gets the same checks as a single-version header. It also adds a test for multi-version headers. The existing parametrized test builds the expected message from the whole line, so it only covers single versions.

All current PEPs still pass python check-peps.py.