message: Fix an invalid pipe to FileCheck in optional.mlir
diff: -// RUN: flatbuffer_translate -mlir-to-tflite-flatbuffer %s -o - | flatbuffer_to_string -
  -// | FileCheck %s
  +// RUN: flatbuffer_translate -mlir-to-tflite-flatbuffer %s -o - | flatbuffer_to_string - | FileCheck %s
  func @main(%arg0: tensor<40x37xf32>, %arg1: tensor<40x37xf32>) -> tensor<40x40xf32> {
  %cst = constant unit
  @@ -9,7 +8,7 @@ func @main(%arg0: tensor<40x37xf32>, %arg1: tensor<40x37xf32>) -> tensor<40x40xf
  return %2 : tensor<40x40xf32>
  }
  -// CHECK-NEXT: operators: [ {
  +// CHECK: operators: [ {
  // CHECK-NEXT: inputs: [ 0, 1, -1 ],
  // CHECK-NEXT: outputs: [ 2, 3 ],
  // CHECK-NEXT: builtin_options_type: FullyConnectedOptions,
  