Update Dependabot configuration for daily security updates

Author: nowsprinting

.github/dependabot.yml

@@ -3,4 +3,5 @@ updates:
   - package-ecosystem: github-actions
     directory: /
     schedule:
-      interval: weekly
+      interval: daily
+    open-pull-requests-limit: 0   # security updates only. refs https://docs.github.com/ja/code-security/dependabot/dependabot-security-updates/configuring-dependabot-security-updates#overriding-the-default-behavior-with-a-configuration-file