fix!: Time::setTimestamp()'s different behavior than DateTime

Author: kenjis

system/I18n/TimeTrait.php

@@ -697,9 +697,7 @@ public function setTimezone($timezone)
     #[ReturnTypeWillChange]
     public function setTimestamp($timestamp)
     {
-        $time = date('Y-m-d H:i:s', $timestamp);
-
-        return static::parse($time, $this->timezone, $this->locale);
+        return parent::setTimestamp($timestamp);
     }
 
     // --------------------------------------------------------------------

tests/system/I18n/TimeTest.php

@@ -18,6 +18,7 @@
 use CodeIgniter\Test\CIUnitTestCase;
 use Config\App;
 use DateTime;
+use DateTimeImmutable;
 use DateTimeZone;
 use IntlDateFormatter;
 use Locale;
@@ -719,13 +720,28 @@ public function testSetTimezone(): void
 
     public function testSetTimestamp(): void
     {
-        $time  = Time::parse('May 10, 2017', 'America/Chicago');
-        $stamp = strtotime('April 1, 2017');
-        $time2 = $time->setTimestamp($stamp);
+        $time1 = Time::parse('May 10, 2017', 'America/Chicago');
+
+        $stamp = strtotime('2017-04-01'); // We use UTC as the default timezone.
+        $time2 = $time1->setTimestamp($stamp);
 
         $this->assertInstanceOf(Time::class, $time2);
-        $this->assertNotSame($time, $time2);
-        $this->assertSame('2017-04-01 00:00:00', $time2->toDateTimeString());
+        $this->assertSame('2017-05-10 00:00:00 -05:00', $time1->format('Y-m-d H:i:s P'));
+        $this->assertSame('2017-03-31 19:00:00 -05:00', $time2->format('Y-m-d H:i:s P'));
+    }
+
+    public function testSetTimestampDateTimeImmutable(): void
+    {
+        $time1 = new DateTimeImmutable(
+            'May 10, 2017',
+            new DateTimeZone('America/Chicago')
+        );
+
+        $stamp = strtotime('2017-04-01'); // We use UTC as the default timezone.
+        $time2 = $time1->setTimestamp($stamp);
+
+        $this->assertSame('2017-05-10 00:00:00 -05:00', $time1->format('Y-m-d H:i:s P'));
+        $this->assertSame('2017-03-31 19:00:00 -05:00', $time2->format('Y-m-d H:i:s P'));
     }
 
     public function testToDateString(): void