⬆️ Configure dependabot to ignore Python version updates

Python version should be constrained by the anaconda distribution version
specified in environment.yml, not updated independently by dependabot.

Author: mmcky

.github/dependabot.yml

@@ -21,3 +21,5 @@ updates:
     ignore:
       - dependency-name: "jupyter-book"
         versions: [">=2.0"]
+      - dependency-name: "python"
+        # Python version should be constrained by the anaconda distribution version