Drop pdm.lock from pre-commit for uv-managed repos

Description

Doesn't drop pdm completely as we still need it in CI for building the locked version of the package, but moving towards dropping it completely when using uv as our package manager.

Checklist

Please confirm that this pull request has done the following:

• Tests added (but see https://github.com/openscm/pandas-openscm/pull/8)
• Documentation added (where applicable)
• Changelog item added to changelog/