Ensure unlock wait after saving working copy changes in Cypress tests

[wesleybl]

This fixes the error:

1) Working Copy Tests - Applying
       Basic apply operation:
     AssertionError: Timed out retrying after 4000ms: Expected to find content: 'Changes applied' but never did.
      at Context.eval (webpack://@plone/volto/./cypress/tests/workingCopy/applying.js:45:7)

See: https://github.com/plone/volto/actions/runs/23294919481/job/67739734466#step:4:212

[davisagli]

This is fine, but note that there's a real race condition here too. If the save finishes before the unlock, then the actions menu does not include the options for applying or canceling the working copy.

To avoid that I'd like to add a way to unlock the item in the same transaction where it is saved, via a special header.