Fix #21532: Check if template return is untyped (#22517)

* Don't ignore return in semTemplateDef

* Add test

---------

Co-authored-by: SirOlaf <>

tests/template/t21532.nim

@@ -0,0 +1,8 @@
+
+template elementType(a: untyped): typedesc =
+  typeof(block: (for ai in a: ai))
+
+func fn[T](a: T) =
+  doAssert elementType(a) is int
+
+@[1,2,3].fn