docs: require sphinx-rtd-theme>=0.5.2 and the latest pip to prevent installing...

docs: require sphinx-rtd-theme>=0.5.2 and the latest pip to prevent installing breaking docutils>=0.17

.readthedocs.yml

@@ -12,6 +12,5 @@ python:
   # https://docs.readthedocs.io/en/stable/config-file/v2.html#build-image
   version: 3.8  # Keep in sync with .github/workflows/checks.yml
   install:
-    - requirements: docs/pip.txt
     - requirements: docs/requirements.txt
     - path: .

docs/pip.txt

-# In pip 20.3-21.0, the default dependency resolver causes the build in
-# ReadTheDocs to fail due to memory exhaustion or timeout.
-pip<20.3

docs/requirements.txt

 Sphinx>=3.0
 sphinx-hoverxref>=0.2b1
 sphinx-notfound-page>=0.4
-sphinx_rtd_theme>=0.4
+sphinx-rtd-theme>=0.5.2
\ No newline at end of file