build(deps): bump pytest from 7.4.4 to 8.0.0 in /lib/spack/docs (#42361)

Bumps [pytest](https://github.com/pytest-dev/pytest) from 7.4.4 to 8.0.0.
- [Release notes](https://github.com/pytest-dev/pytest/releases)
- [Changelog](https://github.com/pytest-dev/pytest/blob/main/CHANGELOG.rst)
- [Commits](https://github.com/pytest-dev/pytest/compare/7.4.4...8.0.0)

---
updated-dependencies:
- dependency-name: pytest
  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

@@ -6,7 +6,7 @@ python-levenshtein==0.23.0
 docutils==0.20.1
 pygments==2.17.2
 urllib3==2.1.0
-pytest==7.4.4
+pytest==8.0.0
 isort==5.13.2
 black==24.1.1
 flake8==7.0.0