fix(tests): Ensure reliable CUDA cache clearing in MoE test (#23416)

Signed-off-by: AzizCode92 <azizbenothman76@gmail.com>
Signed-off-by: Michael Goin <mgoin64@gmail.com>
Co-authored-by: Michael Goin <mgoin64@gmail.com>
Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

tests/kernels/moe/test_moe.py

@@ -429,11 +429,11 @@ def test_mixtral_moe(dtype: torch.dtype, padding: bool, use_rocm_aiter: bool,
                 vllm_moe.experts.w13_weight, (0, 128), "constant", 0)[...,
                                                                       0:-128],
                                                     requires_grad=False)
-            torch.cuda.empty_cache()
             vllm_moe.experts.w2_weight = Parameter(F.pad(
                 vllm_moe.experts.w2_weight, (0, 128), "constant", 0)[...,
                                                                      0:-128],
                                                    requires_grad=False)
+            torch.cuda.synchronize()
             torch.cuda.empty_cache()
 
         # Run forward passes for both MoE blocks