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

[kasperk81]

@tannergooding, @michaelgsharp, @carlossanlop
another new .net 9 api bug fix. is backport warranted for this pr?

[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);