build(deps): bump isort from 5.12.0 to 5.13.2 in /lib/spack/docs (#41651)

Bumps [isort](https://github.com/pycqa/isort) from 5.12.0 to 5.13.2.
- [Release notes](https://github.com/pycqa/isort/releases)
- [Changelog](https://github.com/PyCQA/isort/blob/main/CHANGELOG.md)
- [Commits](https://github.com/pycqa/isort/compare/5.12.0...5.13.2)

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

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

@@ -7,7 +7,7 @@ docutils==0.20.1
 pygments==2.17.2
 urllib3==2.1.0
 pytest==7.4.3
-isort==5.12.0
+isort==5.13.2
 black==23.11.0
 flake8==6.1.0
 mypy==1.7.1