Fix: Consider bot message on slack integration (#6793)

lib/integrations/slack/send_on_slack_service.rb

@@ -9,7 +9,7 @@ class Integrations::Slack::SendOnSlackService < Base::SendOnChannelService
     # we don't want message loop in slack
     return if message.external_source_id_slack.present?
     # we don't want to start slack thread from agent conversation as of now
-    return if message.outgoing? && conversation.identifier.blank?
+    return if invalid_message?
 
     perform_reply
   end
@@ -23,6 +23,10 @@ class Integrations::Slack::SendOnSlackService < Base::SendOnChannelService
     true
   end
 
+  def invalid_message?
+    (message.outgoing? && conversation.identifier.blank?) || !message.slack_hook_sendable?
+  end
+
   def perform_reply
     send_message