CI: Bump to mambaforge-22.9 in ReadTheDocs (#3268)

Author: seisman

.readthedocs.yaml

@@ -8,7 +8,7 @@ version: 2
 build:
   os: ubuntu-22.04
   tools:
-    python: "mambaforge-4.10"
+    python: "mambaforge-22.9"
   jobs:
     post_checkout:
       # Cancel building pull requests when there aren't changes related to docs.