mbstring: Fix mb_rtrim() for UTF-8 text

Author: nsfisis

src/Mbstring/Mbstring.php

@@ -983,7 +983,7 @@ public static function mb_ltrim(string $string, ?string $characters = null, ?str
 
     public static function mb_rtrim(string $string, ?string $characters = null, ?string $encoding = null): string
     {
-        return self::mb_internal_trim('{[%s]+$}D', $string, $characters, $encoding, __FUNCTION__);
+        return self::mb_internal_trim('{[%s]+$}Du', $string, $characters, $encoding, __FUNCTION__);
     }
 
     private static function mb_internal_trim(string $regex, string $string, ?string $characters, ?string $encoding, string $function): string

tests/Mbstring/MbstringTest.php

@@ -886,6 +886,7 @@ public static function mbLTrimProvider(): iterable
         yield [' test ', ' test ', ''];
 
         yield ['いああああ', 'あああああああああああああああああああああああああああああああああいああああ', 'あ'];
+        yield ['あいうえお　', '　あいうえお　'];
 
         yield ['漢字', "\u{FFFE}漢字", "\u{FFFE}\u{FEFF}"];
         yield [' abcd ', ' abcd ', ''];
@@ -902,6 +903,7 @@ public static function mbRTrimProvider(): iterable
         yield ['                                                                                                                                 a', str_repeat(' ', 129).'a'];
 
         yield ['あああああああああああああああああああああああああああああああああい', 'あああああああああああああああああああああああああああああああああいああああ', 'あ'];
+        yield ['　あいうえお', '　あいうえお　'];
 
         yield [' abcd ', ' abcd ', ''];