build(deps): bump black from 24.10.0 to 25.1.0 in /lib/spack/docs (#48780)

Bumps [black](https://github.com/psf/black) from 24.10.0 to 25.1.0.
- [Release notes](https://github.com/psf/black/releases)
- [Changelog](https://github.com/psf/black/blob/main/CHANGES.md)
- [Commits](https://github.com/psf/black/compare/24.10.0...25.1.0)

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

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

lib/spack/docs/requirements.txt

@@ -8,6 +8,6 @@ pygments==2.19.1
 urllib3==2.3.0
 pytest==8.3.4
 isort==5.13.2
-black==24.10.0
+black==25.1.0
 flake8==7.1.1
 mypy==1.11.1