Update readthedocs.yml

Further attempts to fix #638, by moving to the Conda release of Python

Author: davidwagner

readthedocs.yml

@@ -5,7 +5,7 @@ formats: all
 build:
   os: ubuntu-24.04
   tools:
-    python: "3.6"
+    python: "miniconda-3.12-24.9"
 
 sphinx:
   configuration: docs/conf.py