fix!: now Time::createFromTimestamp() returns Time with UTC by default

Author: kenjis

system/I18n/TimeTrait.php

@@ -269,7 +269,7 @@ public static function createFromTimestamp(int $timestamp, $timezone = null, ?st
     {
         $time = new self(gmdate('Y-m-d H:i:s', $timestamp), 'UTC', $locale);
 
-        $timezone ??= date_default_timezone_get();
+        $timezone ??= 'UTC';
 
         return $time->setTimezone($timezone);
     }

tests/system/I18n/TimeTest.php

@@ -277,10 +277,11 @@ public function testCreateFromTimestamp(): void
 
         $timestamp = strtotime('2017-03-18 midnight');
 
+        // The timezone will be UTC if you don't specify.
         $time = Time::createFromTimestamp($timestamp);
 
-        $this->assertSame('Asia/Tokyo', $time->getTimezone()->getName());
-        $this->assertSame('2017-03-18 00:00:00', $time->format('Y-m-d H:i:s'));
+        $this->assertSame('UTC', $time->getTimezone()->getName());
+        $this->assertSame('2017-03-17 15:00:00', $time->format('Y-m-d H:i:s'));
 
         // Restore timezone.
         date_default_timezone_set($tz);