In the web client, in a real use case, it's not possible
to write on fields which are invisible,
as it's not possible to write on fields which are readonly.

This is a first step in the goal to change the behavior
of the `groups=` attribute in the back-end views,
to remove them for the view instead of making them invisible.

This is mainly to reduce the diff of the revision that will introduce
the mentioned above behavior change.

As nodes with `groups=` will be removed from the view
when the user doesn't have the group, it's no longer possible
to set a value on a field having a `groups=` the user doesn't have
in the `Form` test class, as the field will no longer be at all in the
view.
However, these unit tests shouldn't have been able to set values
on invisible fields in the first place.
This revision therefore aims to correct the unit tests setting value
on fields which were invisible because the user executing the
test was not part of the required group(s) for these fields
to be visible in the view.