Python: Fix inefficient string comparison

python/ql/test/extractor-tests/flags/Flags.ql

@@ -1,9 +1,8 @@
-
 import python
 
 from string k, string v
-where k.prefix(8) = "options." and
-not k.prefix(14) = "options.verbos" and
-py_flags_versioned(k, v, _)
+where
+  not k.matches("options.%") and
+  not k.matches("options.verbos%") and
+  py_flags_versioned(k, v, _)
 select k, v
-