Add tzdata requirement on Windows

[MinchinWeb]

Further to #3161, tzdata is required on Windows, even when using a version of Python that includes zoneinfo in the standard library. This is because Windows doesn't ship with the "standard" timezone database; c.f. PEP 615.

Without this, Pelican 4.9.0 will spit out a series of errors (one for each entry), like:

[10:53:22] ERROR    Could not process .\20121024-push-a-hg-repo-to-github.md                                   log.py:94
                    'No time zone found with key America/Edmonton'

and then finally has a fatal error:

           CRITICAL ZoneInfoNotFoundError: 'No time zone found with key UTC'                             __init__.py:666

I also note that tzdata is listed as a requirement for testing; it may no longer be needed there.

[avaris]

I also note that tzdata is listed as a requirement for testing; it may no longer be needed there.

I was confused a bit. I was going to say it should show up in tests but that's why tests were passing :). I think it should be removed from test.pip.

[MinchinWeb]

I think it should be removed from test.pip.

done!

[MinchinWeb]

FYI, here's where tzdata was added to the testing requirements: 91d9ef7

Add tzdata as dependency in test requirements

Otherwise yields the following error with Python 3.10 on Windows:

zoneinfo._common.ZoneInfoNotFoundError: 'No time zone found with key UTC'

[justinmayer]

Sorry for this snafu. When I first saw this error, I read something on the Internet that gave me the (clearly-mistaken) impression that the tzdata dependency was something that only needed to be addressed when testing on Windows and that was not otherwise necessary to use Pelican on Windows. Mea culpa.

Many thanks to @MinchinWeb for the fix and to @avaris for reviewing.

[MinchinWeb]

No worries @justinmayer ! You and avaris do a great job of keeping the project moving forward, and make it easy to contribute, and this is still a timely fix. Mostly I just got a little chuckle that I wasn't able to help with your 3.9 release sprint, but instead found this the next day.