Re-allow underscore on valid_url_path_ending_chars (#4999)

Limiting allowed characters in the last character of the URL is came from twitter-text, but underscore is allowed on there, and Mastodon before #4941.

config/initializers/twitter_regex.rb

@@ -2,7 +2,7 @@ module Twitter
   class Regex
 
     REGEXEN[:valid_general_url_path_chars] = /[^\p{White_Space}\(\)\?]/iou
-    REGEXEN[:valid_url_path_ending_chars] = /[^\p{White_Space}\(\)\?!\*';:=\,\.\$%\[\]\p{Pd}_~&\|@]|(?:#{REGEXEN[:valid_url_balanced_parens]})/iou
+    REGEXEN[:valid_url_path_ending_chars] = /[^\p{White_Space}\(\)\?!\*';:=\,\.\$%\[\]\p{Pd}~&\|@]|(?:#{REGEXEN[:valid_url_balanced_parens]})/iou
     REGEXEN[:valid_url_balanced_parens] = /
       \(
         (?: