ci: Add dependency cooldown

Use dependency cooldown to mitigate supply chain attacks.

Signed-off-by: Dariusz Frankiewicz <[email protected]>

Author: dariusz-f

.github/dependabot.yml

@@ -4,3 +4,5 @@ updates:
     directory: /
     schedule:
       interval: weekly
+    cooldown:
+      default-days: 14