activerecord: Allow comment prefix in queries when preventing writes

[dylanahsmith]

@rafaelfranca

Problem

We use marginalia attach comments to queries to help provide context for queries in the slow query log. We also use Marginalia::Comment.prepend_comment = true to prepend the comment so it isn't lost from truncation. However, this resulted in the ActiveRecord::ConnectionAdapters::MySQL::DatabaseStatements::READ_QUERY to no longer match any queries, which would prevent any queries from being performed on a database connection configured with replica: true due to it trying to prevent write queries.

Solution

Update the regex to ignore /* ... */ comments at the start of the query string.

[eugeneius]

Backported to 6-0-stable in 290e485.