Fix CI not running on MySQL 5.5

```
% bin/test -w -a mysql2
Using mysql2
/Users/kamipo/src/github.com/rails/rails/vendor/bundle/ruby/3.0.0/bundler/gems/mysql2-7f4e844fccf6/lib/mysql2/client.rb:131:in `_query': Mysql2::Error: The used table type doesn't support FULLTEXT indexes (ActiveRecord::StatementInvalid)
```

Author: kamipo

activerecord/test/schema/mysql2_specific_schema.rb

@@ -47,7 +47,7 @@
     t.index :var_binary
   end
 
-  create_table :key_tests, force: true do |t|
+  create_table :key_tests, force: true, options: "ENGINE=MyISAM" do |t|
     t.string :awesome
     t.string :pizza
     t.string :snacks