... this breaks the Rails 5 upgrade, and it's actually no longer needed.
New installations will have the right size anyway, and even if some
older installations miss the migration by not updating for 2 years, it
still doesn't matter since there is no risk that we will ever have
emojis in our migration filenames.
mysql changes the type of TEXT columns to MEDIUMTEXT with "CONVERT TO",
but we don't want this, so change this columns back to TEXT.
see: https://bugs.mysql.com/bug.php?id=31291
Add warning about MySQL collation
Fix database index length
This allows new databases to be created with utf8mb4, on MySQL. The maximum
column size is 767 bytes. Each character is 4 bytes long -> 767 / 4 = 191
characters for the column.
