readthedocs requires build block to be set, see https://docs.readth…

…edocs.io/en/stable/config-file/index.html

.readthedocs.yml

@@ -1,8 +1,15 @@
 # Required
 version: 2
 
+# Set the version of Python and other tools you might need
+build:
+  os: ubuntu-22.04
+  tools:
+    python: "3.8"
+
 # Build documentation in the docs/ directory with Sphinx
 sphinx:
+  builder: html
   configuration: docs/source/conf.py
   fail_on_warning: false
 
@@ -12,7 +19,6 @@ formats:
 
 # Optionally set the version of Python and requirements required to build your docs
 python:
-  version: 3.8
   install:
     - requirements: docs/requirements.txt
     - requirements: requirements.txt