[promises] Fix flake noticed internally (#34038)

Another case where we need to raise the 'failed before receive
completed' flag prior to actually failing -- I think once promises are
all rolled out I'd like to consider ways to remove this flag.

src/core/lib/surface/call.cc

@@ -3352,6 +3352,7 @@ void ServerPromiseBasedCall::CommitBatch(const grpc_op* ops, size_t nops,
         break;
       case GRPC_OP_RECV_MESSAGE:
         if (cancelled_.load(std::memory_order_relaxed)) {
+          set_failed_before_recv_message();
           FailCompletion(completion);
           break;
         }