ci: add dependabot cooldown

Author: tobiasraabe

.github/dependabot.yml

@@ -5,6 +5,8 @@ updates:
     directory: "/"
     schedule:
       interval: "weekly"
+    cooldown:
+      default-days: 7
     groups:
       github-actions:
         patterns:
@@ -13,3 +15,5 @@ updates:
     directory: "/"
     schedule:
       interval: "weekly"
+    cooldown:
+      default-days: 7