Reduce the number of Dependabot PRs (#592)

* Add Dependabot groups

* Fix comment

* Switch to monthly

Author: zmoon

.github/dependabot.yml

@@ -8,10 +8,17 @@ updates:
   - package-ecosystem: "github-actions" # search for actions
     directory: "/" # search in .github/workflows
     schedule:
-      interval: "weekly" # check for action updates every week
+      interval: "monthly" # check for action updates every month
+    groups:
+      gha-workflow-deps:
+        patterns:
+          - "*"
 
   - package-ecosystem: "pip" # search for requirements.txt
     directory: "/"
     schedule:
-      interval: "weekly" # check for action updates every week
-
+      interval: "monthly" # check for pip dep updates every month
+    groups:
+      pip-deps:
+        patterns:
+          - "*"