build(deps): bump prosemirror-markdown from 1.12.0 to 1.13.0

Bumps [prosemirror-markdown](https://github.com/prosemirror/prosemirror-markdown) from 1.12.0 to 1.13.0.
- [Changelog](https://github.com/ProseMirror/prosemirror-markdown/blob/master/CHANGELOG.md)
- [Commits](ProseMirror/prosemirror-markdown@1.12.0...1.13.0)

---
updated-dependencies:
- dependency-name: prosemirror-markdown
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>