docutils > 0.17 issue with rendering list items in sphinx (#26355)

* downgrade_docutils_version

* invalid version

* Update requirements.txt

* Improve spelling and shorten the reference link

* Update spack.yaml

* update version requirement

* update version to maximum of 0.16

Co-authored-by: bernhardkaindl <43588962+bernhardkaindl@users.noreply.github.com>

lib/spack/docs/requirements.txt

@@ -5,3 +5,6 @@ sphinx>=3.4,!=4.1.2
 sphinxcontrib-programoutput
 sphinx-rtd-theme
 python-levenshtein
+# Restrict to docutils <0.17 to workaround a list rendering issue in sphinx.
+# https://stackoverflow.com/questions/67542699
+docutils <0.17

lib/spack/docs/spack.yaml

@@ -17,6 +17,7 @@ spack:
   # Sphinx
   - "py-sphinx@3.4:4.1.1,4.1.3:"
   - py-sphinxcontrib-programoutput
+  - py-docutils@:0.16
   - py-sphinx-rtd-theme
   # VCS
   - git