Group dependabot updates

Closes #116

Author: dalito

.github/dependabot.yml

@@ -1,6 +1,15 @@
+# This configures updates via dependabot only for github actions.
+# All updates are grouped into a single PR.
+
 version: 2
 updates:
 - package-ecosystem: github-actions
   directory: "/"
   schedule:
     interval: monthly
+  groups:
+    github-actions:
+      patterns:
+        - "*"
+
+# Ref: https://docs.github.com/github/administering-a-repository/configuration-options-for-dependency-updates