Description:
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When using ->setTime() on a DateTime object, the offset may be changed even if the new time is valid in the existing offset.

(Aside: This bug also reveals that with the current API it's actually impossible to use ->setTime() to set some valid time values)

Test script:
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<?php

$tzUK = new DateTimeZone("Europe/London");
$tzUtc = new DateTimeZone("UTC");
$dt = DateTime::createFromFormat("!Y-m-d H:i:s", "2020-10-25 00:05:00", $tzUtc);
$dt = DateTime::createFromFormat('U', $dt->format('U'));

print $dt->format(DateTime::RFC3339 ." e") ."\n";

$dt->setTimeZone($tzUK);

print $dt->format(DateTime::RFC3339 ." e") ."\n";

$dt->setTime((int) $dt->format('H'), (int) $dt->format('i'), 0);

print $dt->format(DateTime::RFC3339 ." e") ."\n";

Expected result:
----------------
2020-10-25T00:05:00+00:00 +00:00
2020-10-25T01:05:00+01:00 Europe/London
2020-10-25T01:05:00+01:00 Europe/London

Actual result:
--------------
2020-10-25T00:05:00+00:00 +00:00
2020-10-25T01:05:00+01:00 Europe/London
2020-10-25T01:05:00+00:00 Europe/London