Fix construction of nested generic tuple return types

Unfortunately this appears to show up a separate bug.

jedi/inference/gradual/base.py

@@ -99,7 +99,7 @@ class DefineGenericBase(LazyValueWrapper):
         for generic_set in self.get_generics():
             values = NO_VALUES
             for generic in generic_set:
-                if isinstance(generic, (GenericClass, TypeVar)):
+                if isinstance(generic, (DefineGenericBase, TypeVar)):
                     result = generic.define_generics(type_var_dict)
                     values |= result
                     if result != ValueSet({generic}):

test/completion/pep0484_generic_parameters.py

@@ -6,6 +6,7 @@ from typing import (
     Iterable,
     List,
     Mapping,
+    Tuple,
     Type,
     TypeVar,
     Union,
@@ -59,6 +60,26 @@ for b in list_type_t_to_list_t(list_of_int_type):
     b
 
 
+# Test construction of nested generic tuple return parameters
+def list_t_to_list_tuple_t(the_list: List[T]) -> List[Tuple[T]]:
+    return [(x,) for x in the_list]
+
+
+x1t = list_t_to_list_tuple_t(list_of_ints)[0][0]
+#? int()
+x1t
+
+
+for c1 in list_t_to_list_tuple_t(list_of_ints):
+    #? int()
+    c1[0]
+
+
+for c2, in list_t_to_list_tuple_t(list_of_ints):
+    #? int()
+    c2
+
+
 def foo(x: T) -> T:
     return x