ci: allow dependabot to update GitHub actions (#250)

Author: sdn4z

.github/dependabot.yml

@@ -20,3 +20,23 @@ updates:
           - "*"
         update-types:
           - "minor"
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+      day: "monday"
+    labels:
+      - "dependencies"
+    commit-message:
+      prefix: "chore"
+    groups:
+      patch-updates:
+        patterns:
+          - "*"
+        update-types:
+          - "patch"
+      minor-updates:
+        patterns:
+          - "*"
+        update-types:
+          - "minor"