tolerate non-types as Tuple parameters better

part of #19998

Author: JeffBezanson

src/subtype.c

@@ -414,7 +414,7 @@ static int is_leaf_bound(jl_value_t *v)
         }
         return 1;
     }
-    return 0;
+    return !jl_is_type(v) && !jl_is_typevar(v);
 }
 
 static jl_value_t *widen_Type(jl_value_t *t)

test/subtype.jl

@@ -938,3 +938,6 @@ ftwoparams(::TwoParams{<:Real,<:Real}) = 3
 # supertype operator
 @test !(Int >: Integer)
 @test Integer >: Int
+
+# tolerate non-types in Tuples
+@test typeintersect(Tuple{0}, Tuple{T} where T) === Tuple{0}