Python: Add test for iterable unpacking on module level

Currently doesn't work :O

python/ql/test/experimental/dataflow/coverage/module_level.py

@@ -0,0 +1,7 @@
+# this test has code on module level, which works in slightly different ways than when
+# inside a function
+
+t = (SOURCE, NONSOURCE)
+a, b = t
+SINK(a) #$ MISSING: flow="SOURCE, l:-2 -> a"
+SINK_F(b)