ci: add dependabot cooldown (#778)

Author: wochinge

.github/dependabot.yml

@@ -9,6 +9,8 @@ updates:
     directory: "/" # Location of package manifests
     schedule:
       interval: "daily"
+    cooldown:
+      default-days: 7
     versioning-strategy: "increase"
     commit-message:
       prefix: chore
@@ -18,6 +20,8 @@ updates:
     directory: "/"
     schedule:
       interval: weekly
+    cooldown:
+      default-days: 7
     commit-message:
       prefix: ci
       include: scope