- make RTD work again

.readthedocs.yaml

@@ -14,3 +14,11 @@ build:
 # Build documentation in the docs/ directory with Sphinx
 sphinx:
   configuration: docs/conf.py
+
+# We recommend specifying your dependencies to enable reproducible builds:
+# https://docs.readthedocs.io/en/stable/guides/reproducible-builds.html
+python:
+  install:
+  - requirements: docs/requirements.txt
+  - method: pip
+    path: .

docs/requirements.txt

+# sphinx_rtd_theme requires docutils < 0.19
+docutils < 0.19
 # sphinxcontrib_zopeext is not compatible with Sphinx 7
-Sphinx < 7
+Sphinx > 6, < 7
 # Silence dependabot claiming a security issue in older versions:
 pygments >= 2.7.4
 docutils
 ZODB
 sphinxcontrib_zopeext
 j1m.sphinxautozconfig
-sphinx_rtd_theme
+# Force a recent version
+sphinx_rtd_theme > 1