[Do not merge] Introduce regression to test out Github RSpec integration

Do not merge, just a test

app/models/account.rb

@@ -66,7 +66,7 @@ class Account < ApplicationRecord
   BACKGROUND_REFRESH_INTERVAL = 1.week.freeze
 
   USERNAME_RE   = /[a-z0-9_]+([a-z0-9_.-]+[a-z0-9_]+)?/i
-  MENTION_RE    = %r{(?<![=/[:word:]])@((#{USERNAME_RE})(?:@[[:word:].-]+[[:word:]]+)?)}i
+  MENTION_RE    = %r{(?<![/[:word:]])@((#{USERNAME_RE})(?:@[[:word:].-]+[[:word:]]+)?)}i
   URL_PREFIX_RE = %r{\Ahttp(s?)://[^/]+}
   USERNAME_ONLY_RE = /\A#{USERNAME_RE}\z/i