bpo-45438: format of inspect.Signature with generic builtins (#29212)

Use types.GenericAlias in inspect.formatannotation to correctly add
type arguments of builtin types to the string representation of
Signatures.

Co-authored-by: Martin Rückl <martin.rueckl@codecentric.de>

Lib/inspect.py

@@ -1325,6 +1325,8 @@ def getargvalues(frame):
 def formatannotation(annotation, base_module=None):
     if getattr(annotation, '__module__', None) == 'typing':
         return repr(annotation).replace('typing.', '')
+    if isinstance(annotation, types.GenericAlias):
+        return str(annotation)
     if isinstance(annotation, type):
         if annotation.__module__ in ('builtins', base_module):
             return annotation.__qualname__