chore(deps): configure Dependabot cooldown

Refs
- https://blog.yossarian.net/2025/11/21/We-should-all-be-using-dependency-cooldowns
- https://docs.github.com/en/code-security/dependabot/working-with-dependabot/dependabot-options-reference#cooldown-
- https://docs.zizmor.sh/audits/#dependabot-cooldown

Author: scop

.github/dependabot.yml

@@ -4,7 +4,11 @@ updates:
     directory: /
     schedule:
       interval: daily
+    cooldown:
+      default-days: 7
   - package-ecosystem: gomod
     directory: /
     schedule:
       interval: daily
+    cooldown:
+      default-days: 7