This commit adds unit tests to check the access of portal user. That is,
we check if the readable fields are only available in read access and
writable fields are available for the edition of the task.
We also check if the other fields in task model raise a AccessError if
the portal user wants to access to one of them.
task-2633229
closes#77156
X-original-commit: 1e7185bcdd8913c006148466dec260b8f6d53c0b