fix: avoid Slack file upload API for fallback messages (#10461)

Skip calling the Slack file upload API for message types such as
fallback (e.g., Facebook and location messages) that lack actual file
data in attachments. This prevents unnecessary API calls and resolves a
Sentry error currently occurring in production.

fixes: https://github.com/chatwoot/chatwoot/issues/10460

lib/integrations/slack/send_on_slack_service.rb

@@ -117,6 +117,8 @@ class Integrations::Slack::SendOnSlackService < Base::SendOnChannelService
   end
 
   def upload_file
+    return unless message.attachments.first.with_attached_file?
+
     result = slack_client.files_upload({
       channels: hook.reference_id,
       initial_comment: 'Attached File!',