#2818 fix RTD build error

Author: bagerard

.readthedocs.yml

@@ -11,10 +11,16 @@ sphinx:
 
 # Optionally set the version of Python and requirements required to build your docs
 python:
-  version: 3.7
+  version: 3.9
   install:
     - requirements: docs/requirements.txt
     # docs/conf.py is importing mongoengine
     # so mongoengine needs to be installed as well
     - method: setuptools
       path: .
+
+# Specify the build environment
+build:
+  os: ubuntu-22.04
+  tools:
+    python: "3.9"