chore: Use "create!" and "save!" bang methods when not checking the result (#5358)

* Use "create!" when not checking for errors on the result
* Use "save!" when not checking the result

app/mailboxes/mailbox_helper.rb

@@ -4,7 +4,7 @@ module MailboxHelper
   def create_message
     return if @conversation.messages.find_by(source_id: processed_mail.message_id).present?
 
-    @message = @conversation.messages.create(
+    @message = @conversation.messages.create!(
       account_id: @conversation.account_id,
       sender: @conversation.contact,
       content: mail_content&.truncate(150_000),