build(deps): bump black from 23.9.1 to 23.10.0 in /lib/spack/docs

Bumps [black](https://github.com/psf/black) from 23.9.1 to 23.10.0.
- [Release notes](https://github.com/psf/black/releases)
- [Changelog](https://github.com/psf/black/blob/main/CHANGES.md)
- [Commits](psf/black@23.9.1...23.10.0)

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

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

lib/spack/docs/requirements.txt

@@ -8,6 +8,6 @@ pygments==2.16.1
 urllib3==2.0.7
 pytest==7.4.2
 isort==5.12.0
-black==23.9.1
+black==23.10.0
 flake8==6.1.0
 mypy==1.6.1