Avoid UnknownTimeZoneError when creating patient from Sample

[ramonski]

Description of the issue/feature this PR addresses

Please merge senaite/senaite.core#1931 first

The code of this PR has changed to rely only on the setter from the datetime field.

This PR avoids that the following traceback occurs:

Traceback:

Traceback (innermost last):
Module ZServer.ZPublisher.Publish, line 144, in publish
Module ZPublisher.mapply, line 85, in mapply
Module ZServer.ZPublisher.Publish, line 44, in call_object
Module senaite.app.listing.view, line 223, in call
Module senaite.app.listing.ajax, line 109, in handle_subpath
Module senaite.core.decorators, line 20, in decorator
Module senaite.app.listing.decorators, line 63, in wrapper
Module senaite.app.listing.decorators, line 50, in wrapper
Module senaite.app.listing.decorators, line 100, in wrapper
Module senaite.app.listing.ajax, line 432, in ajax_folderitems
Module senaite.app.listing.decorators, line 88, in wrapper
Module senaite.app.listing.ajax, line 313, in get_folderitems
Module senaite.app.listing.view, line 937, in folderitems
Module senaite.patient.browser.patientfolder, line 116, in folderitem
Module bika.lims.api, line 444, in get_url
Module bika.lims.api, line 268, in is_brain
Module ZODB.Connection, line 795, in setstate
Module ZODB.serialize, line 633, in setGhostState
Module ZODB.serialize, line 626, in getState
Module pytz, line 307, in _p
Module pytz.tzinfo, line 539, in unpickler
Module pytz, line 188, in timezone
UnknownTimeZoneError: (UnknownTimeZoneError('GMT+1',), <function _p at 0x10adda450>, ('GMT+1',))

This happens when a DateTime object was converted with asdatetime and set to the DX datetime field, which resulted in a static timezone like this:

datetime.datetime(1980, 2, 25, 0, 0, tzinfo=<StaticTzInfo 'GMT+1'>)

Current behavior before PR

After instance restart, the patient object could not be deserialized anymore

Desired behavior after PR is merged

Valid datetime object is set as birthdate

--
I confirm I have tested this PR thoroughly and coded it according to PEP8
and Plone's Python styleguide standards.