Fix copy-paste error in Tools/clinic.py (#100560)

Tools/clinic/clinic.py

@@ -2832,7 +2832,7 @@ def modify(self):
         """
         The C statements required to modify this variable after parsing.
         Returns a string containing this code indented at column 0.
-        If no initialization is necessary, returns an empty string.
+        If no modification is necessary, returns an empty string.
         """
         return ""