Increase Dependabot cooldown from the default of 3 days to 7, as [required by zizmor](https://docs.zizmor.sh/audits/#rulesdependabot-cooldownconfigdays).

Author: cpovirk

.github/dependabot.yml

@@ -4,6 +4,8 @@ updates:
     directory: "/"
     schedule:
       interval: "weekly"
+    cooldown:
+      default-days: 7
     groups:
       dependencies:
         applies-to: version-updates
@@ -13,6 +15,8 @@ updates:
     directory: "/"
     schedule:
       interval: "monthly"
+    cooldown:
+      default-days: 7
     groups:
       github-actions:
         applies-to: version-updates