fix(docker): restore daily Dependabot schedule (#5430)

## What changed

Restores the Docker Dependabot cron expression to the known-good
once-daily schedule.

The `supabase/*` cooldown exclusion remains in place, so first-party
Supabase Docker images can still update without the 7-day cooldown.

## Why

The hourly cron expression may be rejected by GitHub Dependabot even
though cron scheduling is documented. Using the existing daily cron
shape avoids breaking Dependabot configuration while preserving the
important first-party cooldown exemption.

Author: jgoux

.github/dependabot.yml

@@ -42,7 +42,7 @@ updates:
     directory: "/apps/cli-go/pkg/config/templates"
     schedule:
       interval: "cron"
-      cronjob: "0 * * * *"
+      cronjob: "0 0 * * *"
     commit-message:
       prefix: "fix(docker): "
     groups: