Bump pymdown-extensions from 10.12 to 10.13 in /.github (#301)

Bumps [pymdown-extensions](https://github.com/facelessuser/pymdown-extensions) from 10.12 to 10.13.
- [Release notes](https://github.com/facelessuser/pymdown-extensions/releases)
- [Commits](facelessuser/pymdown-extensions@10.12...10.13)

---
updated-dependencies:
- dependency-name: pymdown-extensions
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/requirements.txt

@@ -5,7 +5,7 @@ mdx_truly_sane_lists==1.3
 mkdocs==1.6.1
 pygccxml==2.6.1
 Pygments==2.18.0
-pymdown-extensions==10.12
+pymdown-extensions==10.13
 pyplusplus==1.8.5
 setuptools==75.6.0
 six==1.17.0