docs: fix readthedocs config

Author: gadomski

.readthedocs.yml

@@ -5,6 +5,11 @@
 # Required
 version: 2
 
+build:
+  os: ubuntu-22.04
+  tools:
+    python: "mambaforge-22.9"
+
 # Build documentation in the docs/ directory with Sphinx
 sphinx:
   configuration: docs/conf.py
@@ -16,4 +21,4 @@ formats:
   - htmlzip
 
 conda:
-  environment: docs/environment.yml
+  environment: docs/environment.yml