The error in Resque looks like this:
The arguments originally passed to the send_spam_alert function have no symbols in them, so it's not immediately clear why there would be symbols involved. But the installed version of ResqueMailer, 2.4.2, modifies all hashes passed as arguments so that there are two copies of every key/value pair: one where the key is a string, and one where the key is a symbol. This results in the error in send_spam_alert.
In the long run, should help with this. But in the short term, it'd be better to modify send_spam_alert to call with_indifferent_access instead of trying to convert all keys to integers.
Testing Instructions: This should be similar to when it comes to testing. The suggested testing instructions are to deploy to Beta and check for Resque errors.
The latest such error I can find on the queue is dated 2020-07-24, before this fix is deployed. Looks good.