Add changelog entry

changelogs/unreleased/285076-400-bad-request-during-authentication-due-to-password-format-lengt.yml

+---
+title: Add different string encoding method in rack middleware
+merge_request: 49044
+author:
+type: fixed

lib/gitlab/middleware/handle_malformed_strings.rb

@@ -93,7 +93,7 @@ module Gitlab
         # We try to encode the string from ASCII-8BIT to UTF8. If we failed to do
         # so for certain characters in the string, those chars are probably incomplete
         # multibyte characters.
-        string.dup.force_encoding('UTF-8').match?(NULL_BYTE_REGEX)
+        string.dup.force_encoding(Encoding::UTF_8).match?(NULL_BYTE_REGEX)
 
       rescue ArgumentError, Encoding::UndefinedConversionError
         # If we're here, we caught a malformed string. Return true