ci: configure dependabot to update github-actions on a weekly basis

.github/dependabot.yml

@@ -0,0 +1,15 @@
+# To get started with Dependabot version updates, you'll need to specify which
+# package ecosystems to update and where the package manifests are located.
+
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+      day: "monday"
+    commit-message:
+      prefix: "build(dependencies):"
+    groups:
+      github-actions:
+        patterns: [ "*" ]