Address review feedback and strengthen regression coverage

Signed-off-by: Ali Zulfiqar <codewithfourtix@gmail.com>

Author: codewithfourtix

tests/test_requirement_pins.py

@@ -1,3 +1,7 @@
+# Copyright (c) nexB Inc. and others. All rights reserved.
+# SPDX-License-Identifier: Apache-2.0
+# See https://github.com/aboutcode-org/python-inspector for support or download.
+
 import pytest
 
 from packvers.requirements import Requirement