fix: correct Dependabot cooldown configuration

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: sserrata

.github/dependabot.yml

@@ -5,7 +5,7 @@ updates:
     schedule:
       interval: weekly
     cooldown:
-      days: 3
+      default-days: 3
     groups:
       react:
         patterns:
@@ -17,4 +17,4 @@ updates:
     schedule:
       interval: weekly
     cooldown:
-      days: 3
+      default-days: 3