Do not use a binary encoded regexp to avoid warnings

Ref: #43829

```ruby
>> /foo/n.match?("SELECT '€'")
warning: historical binary regexp match /.../n against UTF-8 string
```

The `/n` modifed isn't that necessary anyway, it was just extra caution.

activerecord/lib/active_record/connection_adapters/abstract_adapter.rb

@@ -68,7 +68,7 @@ def self.type_cast_config_to_boolean(config)
       def self.build_read_query_regexp(*parts) # :nodoc:
         parts += DEFAULT_READ_QUERY
         parts = parts.map { |part| /#{part}/i }
-        /\A(?:[(\s]|#{COMMENT_REGEX})*#{Regexp.union(*parts)}/n
+        /\A(?:[(\s]|#{COMMENT_REGEX})*#{Regexp.union(*parts)}/
       end
 
       def self.quoted_column_names # :nodoc: