Python: supress non-useful results (w/ tests) for iter str/seq query

Fixes https://github.com/Semmle/ql/issues/3207

python/ql/src/Statements/IterableStringOrSequence.ql

@@ -12,6 +12,7 @@
  */
 
 import python
+import semmle.python.filters.Tests
 
 predicate has_string_type(Value v) {
     v.getClass() = ClassValue::str()
@@ -28,7 +29,10 @@ where
     iter.pointsTo(seq, seq_origin) and
     has_string_type(str) and
     seq.getClass().isIterable() and
-    not has_string_type(seq)
+    not has_string_type(seq) and
+    // suppress occurrences from tests
+    not seq_origin.getScope().getScope*() instanceof TestScope and
+    not str_origin.getScope().getScope*() instanceof TestScope
 select loop,
     "Iteration over $@, of class " + seq.getClass().getName() + ", may also iterate over $@.",
     seq_origin, "sequence", str_origin, "string"