packagemetadata.py broken.

@christi: patch df8d14ba breaks the pip packaging. Python dependencies are not listed correctly anymore. The Python-Requires keyword in dune.module is missing in the valid_entries list, which is easy to fix but also the regex match string needs to account for '-'.

Testing can be done in dune-common by calling dunepackaging.py --onlysdist

The packages listed in Python-Requires in dune.module should then appear in the generated pyproject.toml