MNT: (deps): Bump pytest-mpl from 0.12 to 0.13 in /ci
MNT: (deps): Bump pytest-mpl from 0.12 to 0.13 in /ci

Bumps [pytest-mpl](https://github.com/matplotlib/pytest-mpl) from 0.12 to 0.13.
- [Release notes](https://github.com/matplotlib/pytest-mpl/releases)
- [Changelog](https://github.com/matplotlib/pytest-mpl/blob/master/CHANGES.md)
- [Commits](https://github.com/matplotlib/pytest-mpl/compare/v0.12.0...v0.13)

---
updated-dependencies:
- dependency-name: pytest-mpl
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@github.com>
Unidata/MetPy,Unidata/MetPy