compiler: add missing break in switch statement (#9901)

Linters don't like this kind of stuff.

compiler/src/java_plugin/cpp/java_generator.cpp

@@ -608,6 +608,7 @@ static void PrintStub(
       break;
     case ABSTRACT_CLASS:
       GRPC_CODEGEN_FAIL << "Call PrintAbstractClassStub for ABSTRACT_CLASS";
+      break;
     default:
       GRPC_CODEGEN_FAIL << "Cannot determine class name for StubType: " << type;
   }