fix(Slack Trigger Node): Fix user ignore filter for message_changed events

[mag123c]

Summary

Fix Usernames or IDs to Ignore filter not working for message_changed events.

When Slack asynchronously enriches messages (e.g., adding locale metadata for non-English languages), it sends a message_changed event where the user ID is in event.message.user instead of event.user. The ignore filter was only checking event.user, causing the filter to fail and resulting in infinite loops.

Now checks both event.user and event.message.user (as fallback).

Related Linear tickets, Github issues, and Community forum posts

Issue: #23782

Review / Merge checklist

• PR title and summary are descriptive. (conventions)
• Docs updated or follow-up ticket created.
• Tests included.
• PR Labeled with release/backport (if the PR is an urgent fix that needs to be backported)

[cubic-dev-ai]

No issues found across 2 files

[n8n-assistant]

Hey @mag123c,

Thank you for your contribution. We appreciate the time and effort you’ve taken to submit this pull request.

Before we can proceed, please ensure the following:
• Tests are included for any new functionality, logic changes or bug fixes.
• The PR aligns with our contribution guidelines.

Regarding new nodes:
We no longer accept new nodes directly into the core codebase. Instead, we encourage contributors to follow our Community Node Submission Guide to publish nodes independently.

If your node integrates with an AI service that you own or represent, please email nodes@n8n.io and we will be happy to discuss the best approach.

About review timelines:
This PR has been added to our internal tracker as "GHC-6172". While we plan to review it, we are currently unable to provide an exact timeframe. Our goal is to begin reviews within a month, but this may change depending on team priorities. We will reach out when the review begins.

Thank you again for contributing to n8n.