Adding default TZ of UTC if none specified in the source data

[BillWeissABK]

Some TLDs (or maybe registrars?) don't provide a timezone for datetimes, which leaves us with two different output types when parsing (reported in #183). This means users of the library have to handle the two paths themselves. This PR adds a timezone of UTC to any that wouldn't have them.

[BillWeissABK]

Unsurprisingly this causes a few test failures with domains that don't currently have a TZ set. I find the error output a little weird, so I'm leaving a note here and pulling those test changes into a new commit in case I'm doing something wrong.

❯ python -m unittest
.............google.com.ua 	(expiration_date):	 2019-12-04 00:00:00+02 != 2019-12-04 00:00:00
google.com.ua 	(creation_date):	 ['2002-12-04 00:00:00+02', '2017-07-28 23:53:31+03'] != ['2002-12-04 00:00:00', '2017-07-28 23:53:31']
google.com.ua 	(updated_date):	 2018-11-02 11:29:08+02 != 2018-11-02 11:29:08
google.com.tr 	(expiration_date):	 2019-Aug-22. != 2019-08-22 00:00:00
google.com.tr 	(creation_date):	 2001-Aug-23. != 2001-08-23 00:00:00
google.cl 	(expiration_date):	 2019-11-20 14:48:02 CLST != 2019-11-20 14:48:02
google.cl 	(creation_date):	 2002-10-22 17:48:23 CLST != 2002-10-22 17:48:23
web.de 	(updated_date):	 ['2016-04-11 11:09:54+02:00', '2011-08-10 17:09:10+02:00'] != ['2016-04-11 11:09:54', '2011-08-10 17:09:10']
google.de 	(updated_date):	 2018-03-12 21:44:25+01:00 != 2018-03-12 21:44:25
F...........2024-04-02 09:11:47,435 - whois.whois - ERROR - Error trying to connect to socket: closing socket - [Errno 61] Connection refused
.
======================================================================
FAIL: test_com_allsamples (test.test_parser.TestParser.test_com_allsamples)
Iterate over all of the sample/whois/*.com files, read the data,
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/bweiss/repos/py-whois/test/test_parser.py", line 117, in test_com_allsamples
    self.fail(
AssertionError: 9/357 sample whois attributes were not parsed properly!

----------------------------------------------------------------------
Ran 26 tests in 3.214s

FAILED (failures=1)

[BillWeissABK]

Tests run cleanly now, only had to make a couple of changes. Seems ok? Reviews appreciated :)