Added native int as Hint test (filtered)

One may think that it would be valid to pass a dict with
an int as key that matches the Hints in libzim's item.h.

Those are filtered in pylibzim as not recognized as Hint objects.

tests/test_libzim_creator.py

@@ -605,6 +605,7 @@ def test_hints_values(fpath):
         c.add_item(StaticItem(path="5", title="", hints={5: True}))
         c.add_item(StaticItem(path="6", title="", hints={"yolo": True}))
         c.add_item(StaticItem(path="7", title="", hints={"FRONT_ARTICLE": True}))
+        c.add_item(StaticItem(path="8", title="", hints={0: True}))
 
         # non-existent Hint
         with pytest.raises(AttributeError, match="YOLO"):