Add missing return

[skojin]

Add missing return to already existing 'head :ok' in controller

to fix

TypeError (no implicit conversion of nil into String):

/usr/local/lib/ruby/3.2.0/openssl/digest.rb:42:in `update'
/usr/local/lib/ruby/3.2.0/openssl/digest.rb:42:in `hexdigest'
/usr/local/lib/ruby/3.2.0/openssl/digest.rb:42:in `block (3 levels) in <class:Digest>'
actionmailbox (7.1.5.1) app/models/action_mailbox/inbound_email/message_id.rb:17:in `create_and_extract_message_id!'
action_mailbox_amazon_ingress (0.1.3) app/controllers/action_mailbox/ingresses/amazon/inbound_emails_controll