chore: mark Kokoro Graalvm checks as required

Author: mpeddada1

.github/sync-repo-settings.yaml

@@ -16,6 +16,9 @@ branchProtectionRules:
       - dependencies (11)
       - clirr
       - cla/google
+      - 'Kokoro - Test: Java GraalVM Native Image A'
+      - 'Kokoro - Test: Java GraalVM Native Image B'
+      - 'Kokoro - Test: Java GraalVM Native Image C'
   - pattern: 1.39.2-sp
     isAdminEnforced: true
     requiredApprovingReviewCount: 1