PicklingError when editing basic tile that contains an image

[wesleybl]

In master, when a basic tile contains an image, and we try to edit it, we get the error:

2022-02-09 09:45:12,958 ERROR   [Zope.SiteErrorLog:252][waitress-0] 1644410712.95793580.7818704923821704 http://localhost:8080/Plone/capa/@@edit-tile/collective.cover.basic/b7af377a-124f-46f5-859e-995ac3b67a20
Traceback (innermost last):
  Module ZPublisher.WSGIPublisher, line 168, in transaction_pubevents
  Module transaction._manager, line 257, in commit
  Module transaction._manager, line 134, in commit
  Module transaction._transaction, line 282, in commit
  Module transaction._compat, line 49, in reraise
  Module transaction._transaction, line 273, in commit
  Module transaction._transaction, line 456, in _commitResources
  Module transaction._compat, line 49, in reraise
  Module transaction._transaction, line 430, in _commitResources
  Module ZODB.Connection, line 497, in commit
  Module ZODB.Connection, line 546, in _commit
  Module ZODB.Connection, line 578, in _store_objects
  Module ZODB.serialize, line 430, in serialize
  Module ZODB.serialize, line 439, in _dump
_pickle.PicklingError: Can't pickle <class 'z3c.form.interfaces.NOT_CHANGED'>: it's not the same object as z3c.form.interfaces.NOT_CHANGED