Adapt tests to changes in mautic/mautic#12813

[mollux]

In https://github.com/mautic/mautic/pull/12813 some logic changed, and it is now required to pass the PostAction in the payload of form API calls.

IMO this is a breaking change, and the default on the Mautic should change to something that is compatible with the previous flow.

If we want to change that default, it needs to be done in M6. This PR is purely meant to show where the issue with the tests is located, not to be merged.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (fa141f9) 52.49% compared to head (5ece05d) 52.49%.

:exclamation: Current head 5ece05d differs from pull request most recent head 404da02. Consider uploading reports for the commit 404da02 to get more accurate results

Additional details and impacted files

@@            Coverage Diff            @@
##               main     #320   +/-   ##
=========================================
  Coverage     52.49%   52.49%           
  Complexity      390      390           
=========================================
  Files            30       30           
  Lines          1042     1042           
=========================================
  Hits            547      547           
  Misses          495      495           

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[mollux]

@kuzmany it shouldn't look good, see the description :) this should be addressed in mautic/mautic, so this change isn't needed

[kuzmany]

Ah, okay I have to check it.

[RCheesley]

Converting this to draft given we don't actually need to do anything with it.