Arm backend: Add missing default case in executor_runner (#15895)

Signed-off-by: per.held@arm.com

Author: perheld

examples/arm/executor_runner/arm_executor_runner.cpp

@@ -470,6 +470,10 @@ Error prepare_input_tensors(
                 tensor.mutable_data_ptr<int8_t>() + tensor.numel(),
                 1);
             break;
+          default:
+            ET_LOG(Error, "Unhandled ScalarType");
+            err = Error::InvalidArgument;
+            break;
         }
       } else {
         printf("Input[%d]: Not Tensor\n", i);