Add main for merge state tests (#6492)

Co-authored-by: luoyuan.luo <luoyuan.luo@antgroup.com>

sgl-kernel/tests/test_merge_state.py

@@ -136,3 +136,7 @@ def test_merge_state(seq_len, num_heads, head_dim):
 
     assert torch.allclose(v_merged, v_merged_std, atol=1e-2)
     assert torch.allclose(s_merged, s_merged_std, atol=1e-2)
+
+
+if __name__ == "__main__":
+    pytest.main([__file__])