Potential fix for code scanning alert no. 9893: Unused local variable

Co-authored-by: Copilot Autofix powered by AI <62310815+github-advanced-security[bot]@users.noreply.github.com>
Signed-off-by: Jinzhe Zeng <njzjz@qq.com>

Author: njzjz

source/tests/tf/test_stat_file.py

@@ -59,8 +59,6 @@ def test_stat_file_tf(self) -> None:
             self.assertTrue(stat_path.exists(), "Stat file directory should be created")
 
             # Check for energy bias and std files
-            bias_file = stat_path / "bias_atom_energy"
-            std_file = stat_path / "std_atom_energy"
 
             # At minimum, the directory structure should be created
             # Even if files aren't created due to insufficient data, the directory should exist