When datetime object DateTimeImmutable, SyslogUdpHandler still doesn't respect TimeZone

[yi-yang-github]

Monolog version 2

This is a followup to #1350

The old fix mainly is here: 226bc5f#diff-ea99f2625937f8253eb05c4bd9cc5aae307e306bf62665c6a809c126b78606f9R98

Which does

$datetime->setTimezone(new \DateTimeZone('UTC'));
...
$date = $datetime->format($this->dateFormats[$this->rfc]);

However, the $datetime object could be \DateTimeImmutable or \DateTime, when it is \DateTimeImmutable, which is, by definition, immutable and the $datetime->setTimezone(new \DateTimeZone('UTC')) function won't be able to change the original $datetime object.

If I add some print_r() here, you can see it's not changed:

M d H:i:s
before: Monolog\DateTimeImmutable Object
(
    [useMicroseconds:Monolog\DateTimeImmutable:private] => 1
    [date] => 2021-03-11 14:47:24.195319
    [timezone_type] => 3
    [timezone] => America/Vancouver
)
Mar 11 14:47:24
after: Monolog\DateTimeImmutable Object
(
    [useMicroseconds:Monolog\DateTimeImmutable:private] => 1
    [date] => 2021-03-11 14:47:24.195319
    [timezone_type] => 3
    [timezone] => America/Vancouver
)
Mar 11 14:47:24

However, if I add something like

            $dateNew = $datetime->setTimezone(new \DateTimeZone('UTC'));
            $date = $dateNew->format($this->dateFormats[$this->rfc]);

Then it works:

M d H:i:s
before: Monolog\DateTimeImmutable Object
(
    [useMicroseconds:Monolog\DateTimeImmutable:private] => 1
    [date] => 2021-03-11 14:48:19.095968
    [timezone_type] => 3
    [timezone] => America/Vancouver
)
Mar 11 14:48:19
after: Monolog\DateTimeImmutable Object
(
    [useMicroseconds:Monolog\DateTimeImmutable:private] => 1
    [date] => 2021-03-11 22:48:19.095968
    [timezone_type] => 3
    [timezone] => UTC
)
Mar 11 22:48:19