Allow gather_inputs to work with a derived Inputs class

No behavior change.
diff --git a/tests/scripts/test_psa_constant_names.py b/tests/scripts/test_psa_constant_names.py
index 5780f25..ee909cf 100755
--- a/tests/scripts/test_psa_constant_names.py
+++ b/tests/scripts/test_psa_constant_names.py
@@ -251,9 +251,9 @@
                 if m:
                     self.add_test_case_line(m.group(1), m.group(2))
 
-def gather_inputs(headers, test_suites):
+def gather_inputs(headers, test_suites, inputs_class=Inputs):
     """Read the list of inputs to test psa_constant_names with."""
-    inputs = Inputs()
+    inputs = inputs_class()
     for header in headers:
         inputs.parse_header(header)
     for test_cases in test_suites: