dependabot: Remove deprecated reviewers

See https://github.blog/changelog/2025-04-29-dependabot-reviewers-configuration-option-being-replaced-by-code-owners/

Author: weppos

.github/dependabot.yml

@@ -1,13 +1,11 @@
 ---
 version: 2
 updates:
-  - package-ecosystem: "github-actions"
-    directory: "/"
+  - package-ecosystem: github-actions
+    directory: /
     schedule:
-      interval: "daily"
+      interval: weekly
     open-pull-requests-limit: 10
     labels:
       - task
       - dependencies
-    reviewers:
-      - "dnsimple/platform"