Fix REUSE headers and lint issues in new test

Author: anaslari23

benchexec/tablegenerator/test_href_substitution.py

@@ -1,7 +1,12 @@
-import os
+# This file is part of BenchExec, a framework for reliable benchmarking:
+# https://github.com/sosy-lab/benchexec
+#
+# SPDX-FileCopyrightText: 2007-2026 Dirk Beyer <https://www.sosy-lab.org>
+#
+# SPDX-License-Identifier: Apache-2.0
+
 import unittest
 from benchexec.tablegenerator import htmltable
-from benchexec.tablegenerator.columns import Column
 
 
 class TestHrefSubstitution(unittest.TestCase):