Don't override the timezone when called with a DateTime object

Author: alphp

.gitignore

@@ -23,6 +23,7 @@ Thumbs.db
 #######################
 /.vscode
 /composer.lock
+.phpunit.result.cache
 # vim
 *~
 *.swp

src/php-8.1-strftime.php

@@ -38,9 +38,9 @@ function strftime (string $format, $timestamp = null, ?string $locale = null) :
       } catch (Exception $e) {
         throw new InvalidArgumentException('$timestamp argument is neither a valid UNIX timestamp, a valid date-time string or a DateTime object.', 0, $e);
       }
-    }
 
-    $timestamp->setTimezone(new DateTimeZone(date_default_timezone_get()));
+      $timestamp->setTimezone(new DateTimeZone(date_default_timezone_get()));
+    }
 
     $locale = Locale::canonicalize($locale ?? (Locale::getDefault() ?? setlocale(LC_TIME, '0')));