chore: add V3-experimental to sync-repo-settings (googleapis#1236)

Author: jainsahab

.github/sync-repo-settings.yaml

@@ -112,6 +112,23 @@ branchProtectionRules:
       - OwlBot Post Processor
       - 'Kokoro - Test: Java GraalVM Native Image'
       - 'Kokoro - Test: Java 17 GraalVM Native Image'
+  - pattern: V3-experimental
+    isAdminEnforced: true
+    requiredApprovingReviewCount: 1
+    requiresCodeOwnerReviews: true
+    requiresStrictStatusChecks: false
+    requiredStatusCheckContexts:
+      - dependencies (8)
+      - dependencies (11)
+      - lint
+      - clirr
+      - units (8)
+      - units (11)
+      - 'Kokoro - Test: Integration'
+      - cla/google
+      - OwlBot Post Processor
+      - 'Kokoro - Test: Java GraalVM Native Image'
+      - 'Kokoro - Test: Java 17 GraalVM Native Image'
   - pattern: 2.15.x
     isAdminEnforced: true
     requiredApprovingReviewCount: 1