Skip softmax BF16 test for ROCm (#21162)

### Description

Skip softmax BF16 test for ROCm, because BFloat16 is unsupported by
MIOpen, and `torch.cuda.is_available()` also returns `True` for ROCm.

orttraining/orttraining/test/python/orttraining_test_ortmodule_onnx_ops.py

@@ -148,8 +148,8 @@ def test_onnx_ops(self):
 
     @unittest.skipIf(not torch.cuda.is_bf16_supported(), "Test requires CUDA and BF16 support")
     def test_softmax_bf16_large(self):
-        if not torch.cuda.is_available():
-            # only test bf16 on cuda
+        if torch.version.cuda is None:
+            # Only run this test when CUDA is available, as on ROCm BF16 is not supported by MIOpen.
             return
 
         class Model(torch.nn.Module):
@@ -175,7 +175,7 @@ def forward(self, input):
         data_ort.requires_grad = True
         ort_res = ort_model(input=data_ort)
         ort_res.backward(gradient=init_grad)
-        # compara result
+        # compare result
         torch.testing.assert_close(data_torch.grad, data_ort.grad, rtol=1e-5, atol=1e-4)