chore: migrate dependabot reviewers to CODEOWNERS

Move reviewer configuration from dependabot.yml to CODEOWNERS file
per GitHub's recommended approach. This allows the same reviewers
to be automatically assigned for all PRs, not just Dependabot ones.

See: https://github.com/dependabot/codeowner-migration-action

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: GaryJones

.github/CODEOWNERS

@@ -0,0 +1,3 @@
+# The following teams will get auto-tagged for a review.
+# See https://docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/customizing-your-repository/about-code-owners
+* @Automattic/vip-plugins

.github/dependabot.yml

@@ -13,8 +13,6 @@ updates:
         patterns: ["*"]
     labels:
       - "dependencies"
-    reviewers:
-      - "Automattic/vip-plugins"
     commit-message:
       prefix: "Actions"
       include: "scope"
@@ -37,8 +35,6 @@ updates:
           - "yoast/*"
     labels:
       - "dependencies"
-    reviewers:
-      - "Automattic/vip-plugins"
     commit-message:
       prefix: "Composer"
       include: "scope"