Skip another test file that doesn't run gradcheck for slow gradcheck (pytorch#154852)

Pull Request resolved: pytorch#154852
Approved by: https://github.com/albanD

Author: soulitzer

test/run_test.py

@@ -423,6 +423,7 @@ def _is_cpp_test(test):
     "test_decomp",
     "test_cpp_extensions_jit",
     "test_jit",
+    "test_matmul_cuda",
     "test_ops",
     "test_ops_jit",
     "dynamo/test_recompile_ux",