Update examples for FROM_UNIXTIME_NANOS

[OneRaynyDay]

The documentation originally stated that FROM_UNIXTIME_NANOS would yield a timestamp(9) with time zone, but the example output is not timezoned.

[ebyhr]

Let's use UTC as timezone so that we can understand the function's behavior quickly.

1970-01-01 00:00:00.000000100 UTC
1970-01-01 00:00:00.000001234 UTC
1970-01-01 00:00:00.000001234 UTC
1969-12-31 23:59:59.999998766 UTC

[OneRaynyDay]

@ebyhr There are a couple more instances of timezone examples where they use a different timezone, should we modify those as well?

For example, see FROM_ISO8601_TIMESTAMP documentation:

SELECT from_iso8601_timestamp('2020-05-11');
-- 2020-05-11 00:00:00.000 America/Vancouver

Should be changed to UTC as well?

[ebyhr]

I think there is no need to change FROM_ISO8601_TIMESTAMP because the timezone doesn't affect the timestamp output.