Enable dependabot

However, the cooldown is 1 week longer than the main repo. This allows
us to confirm everything is okay there before it gets to the release
repo.

Author: QuLogic

.github/dependabot.yml

@@ -0,0 +1,13 @@
+---
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+    cooldown:
+      default-days: 14
+    groups:
+      actions:
+        patterns:
+          - "*"