Python: Add test for tricky module member for type-tracking

Local testing shows that the `getDefinition` result for this is a `SSA filter definition`,
and not an `AssignmentDefinition`.

Author: RasmusWL

python/ql/test/experimental/dataflow/typetracking/mymodule.py

@@ -2,3 +2,6 @@
 
 def func():
     return tracked # $tracked
+
+z = tracked # $tracked
+some_func(z) # $tracked

python/ql/test/experimental/dataflow/typetracking/test.py

@@ -54,6 +54,7 @@ def test_import():
     mymodule.x # $tracked
     y = mymodule.func() # $tracked
     y # $tracked
+    mymodule.z # $tracked
 
 # ------------------------------------------------------------------------------
 

python/ql/test/experimental/dataflow/typetracking/tracked.expected

@@ -0,0 +1 @@
+| test.py:57:16:57:25 | Comment # $tracked | Missing result:tracked= |