fix: Time::createFromTimestamp() returns Time with UTC

Author: kenjis

system/I18n/TimeTrait.php

@@ -266,7 +266,8 @@ public static function createFromFormat($format, $datetime, $timezone = null)
     public static function createFromTimestamp(int $timestamp, $timezone = null, ?string $locale = null)
     {
         $time = new self(gmdate('Y-m-d H:i:s', $timestamp), 'UTC', $locale);
-        $timezone ??= 'UTC';
+
+        $timezone ??= date_default_timezone_get();
 
         return $time->setTimezone($timezone);
     }

tests/system/I18n/TimeTest.php

@@ -259,17 +259,21 @@ public function testCreateFromFormatWithInvalidFormat(): void
 
     public function testCreateFromTimestamp(): void
     {
-        // Set the timezone temporarily to UTC to make sure the test timestamp is correct
+        // Save the current timezone.
         $tz = date_default_timezone_get();
-        date_default_timezone_set('UTC');
 
-        $timestamp = strtotime('2017-03-18 midnight');
+        // Change the timezone other than UTC.
+        date_default_timezone_set('Asia/Tokyo'); // +09:00
 
-        date_default_timezone_set($tz);
+        $timestamp = strtotime('2017-03-18 midnight');
 
         $time = Time::createFromTimestamp($timestamp);
 
+        $this->assertSame('Asia/Tokyo', $time->getTimezone()->getName());
         $this->assertSame(date('2017-03-18 00:00:00'), $time->toDateTimeString());
+
+        // Restore timezone.
+        date_default_timezone_set($tz);
     }
 
     public function testCreateFromTimestampWithTimezone(): void