Python: Consistenly use TestScope instead of Test

It's not clear which one is the correct to use, but there were more uses of
TestScope than Test, so I'm assuming that is the right one ¯\_(ツ)_/¯

python/ql/src/Statements/AssertLiteralConstant.ql

@@ -17,7 +17,7 @@ import semmle.python.filters.Tests
 from Assert a, string value
 where
     /* Exclude asserts inside test cases */
-    not a.getScope() instanceof Test and
+    not a.getScope().getScope*() instanceof TestScope and
     exists(Expr test | test = a.getTest() |
         value = test.(IntegerLiteral).getN()
         or