add 7-day cooldown period to dependabot to placate zizmor

.github/dependabot.yml

diff --git a/.github/dependabot.yml b/.github/dependabot.yml
index 5c56314..2e4b964 100644
--- a/.github/dependabot.yml
+++ b/.github/dependabot.yml
@@ -8,3 +8,5 @@
       actions:
         patterns:
           - "*"
+    cooldown:
+      default-days: 7