Fix #8126 (#8712)

This is a temporary fix that will be reworked in a follow up commit
that aims to eliminate the tfExplicit flag from the compiler. The
complete and proper fix was considered too risky for inclusion just
before our 0.19 release.

tests/parser/ttypeclasses.nim

@@ -40,3 +40,7 @@ static:
   assert y isnot tuple
   assert z isnot seq
 
+  # XXX: These cases don't work properly at the moment:
+  # assert type[int] isnot int
+  # assert type(int) isnot int
+