utf-8 emoticons break wikis and posts

Found a few log entries were wikis could not be saved. Here's an example content that cannot be saved:

Hallo 🙂

Here's the corresponding log entry:

Started POST "/pages/finanzen-2018+433326/posts" for 127.0.0.1 at 2018-05-14 05:14:07 -0700
Processing by Page::PostsController#create as JS
  Parameters: {"utf8"=>"✓", "authenticity_token"=>"0yuaQbpdW3p2QQt1M/FouKEJ9/T1TMYHaauv34n1YyvfHYtmZc4HEWwviF7Qy6AkQGWJlDrS3hfXNF4dMkimuw==", "post"=>{"body"=>"[FILTERED]"}, "post_message"=>"Post Message", "page_id"=>"finanzen-2018+433326"}

ActiveRecord::StatementInvalid (Mysql2::Error: Incorrect string value: '\xF0\x9F\x99\x82 w...' for column 'body' at row 1: INSERT INTO `posts` (`body`, `discussion_id`, `page_terms_id`, `user_id`, `body_html`, `created_at`, `updated_at`) VALUES ('Hallo 🙂', ...)

Here's another one in a sightly different context:

Processing by Wiki::WikisController#update as JS
  Parameters: {"utf8"=>"✓", "wiki"=>{"version"=>"15", "body"=>"[FILTERED]"}, "save"=>"Speichern", "id"=>"275618"}
ActiveRecord::StatementInvalid (Mysql2::Error: Incorrect string value: '\xF0\x9F\x98\x8A\x0A\x0A...' for column 'body' at row 1: UPDATE `wikis` SET `user_id` = 305934, `body` = '...' 
...