bug#46722: test-map-into fails

[dick]

> Does the patch below help?

I don't see why it would if this doesn't work:

(let ((lexical-binding t))
  (funcall
   (funcall
    (backquote
     (lambda (arg)
       (lambda () arg)))
    t)))

But clearly `byte-compile` allows things that the interpreter doesn't,
otherwise it'd never have worked for so long.

While I remain leery of the fast and loose scoping here, it was but a red
herring.  The problem lies with the hashing behavior of
`cl--generic-dispatchers`.