Fix readthedocs.yml (#474)

Ref: https://about.readthedocs.com/blog/2024/12/deprecate-config-files-without-sphinx-or-mkdocs-config/

Author: basnijholt

readthedocs.yml

@@ -3,7 +3,14 @@ version: 2
 build:
     os: "ubuntu-22.04"
     tools:
-        python: "mambaforge-4.10"
+        python: "mambaforge-latest"
+    jobs:
+        post_checkout:
+            - git fetch --unshallow || true
+
+sphinx:
+    configuration: docs/source/conf.py
+    builder: dirhtml
 
 conda:
     environment: docs/environment.yml