fix stack 2x2 tensor along dimension 1

[kasperk81]

fix #108615

[kasperk81]

was

System.Numerics.Tensors.Tests.TensorTests.TensorStackTests [FAIL]
  Assert.Equal() Failure: Values differ
  Expected: 10
  Actual:   1

now passing

[MihaZupan]

Does this part have a similar issue ([0] index + outputs being ignored)?

runtime/src/libraries/System.Numerics.Tensors/src/System/Numerics/Tensors/netcore/TensorExtensions.cs

Lines 3494 to 3499 in ba28992

	Tensor<T>[] outputs = new Tensor<T>[tensors.Length];
	for (int i = 0; i < tensors.Length; i++)
	{
	outputs[i] = Tensor.Unsqueeze(tensors[0], dimension);
	}
	return ref Tensor.ConcatenateOnDimension<T>(dimension, tensors, destination);

[jeffhandley]

@tannergooding / @michaelgsharp -- Once this is merged, let's backport it to release/9.0-staging for servicing.

[tannergooding]

/backport to release/9.0-staging

[github-actions]

Started backporting to release/9.0-staging: https://github.com/dotnet/runtime/actions/runs/11956969073

[MihaZupan]

@tannergooding the outputs array here appears to be ignored as well

runtime/src/libraries/System.Numerics.Tensors/src/System/Numerics/Tensors/netcore/TensorExtensions.cs

Lines 3500 to 3505 in d2fdf24

	Tensor<T>[] outputs = new Tensor<T>[tensors.Length];
	for (int i = 0; i < tensors.Length; i++)
	{
	outputs[i] = Tensor.Unsqueeze(tensors[i], dimension);
	}
	return ref Tensor.ConcatenateOnDimension<T>(dimension, tensors, destination);

[tannergooding]

@MihaZupan, indeed. Would you like to get a small fix up?

[MihaZupan]

I can probably look at it next week if need be, just didn't want it to slip through if we're backporting changes.