Labels to be notified in Slack notifications integration not working
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### Summary
Labels to be notified selected in Slack notifications integration are ignored for Pipeline triggers. It seems to work fine if the Note trigger is activated apparently.
### Steps to reproduce
Configure in Slack notifications a webhook with "All branches" selected and an arbitrary label in "Labels to be notified", lets say "~monitored"
create a MR with no labels and an active pipeline and the webhook will be triggered for the pipeline.
### Example Project
https://gitlab.com/virgilx13/slackintegrationexample
### What is the current *bug* behavior?
The webhook is triggered even if the MR doesnt have any of the specified labels in "Labels to be notified"
### What is the expected *correct* behavior?
The webhook should be triggered only if the MR has the label specified.
### Possible fixes
A possible fix is mentioned here: https://gitlab.com/gitlab-org/gitlab/-/issues/387630#note_1333910514.
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### Relevant logs and/or screenshots
### Output of checks
<!-- If you are reporting a bug on GitLab.com, uncomment below -->
This bug happens on GitLab.com
#### Results of GitLab environment info
<!-- Input any relevant GitLab environment information if needed. -->
<details>
<summary>Expand for output related to GitLab environment info</summary>
<pre>
(For installations with omnibus-gitlab package run and paste the output of:
`sudo gitlab-rake gitlab:env:info`)
(For installations from source run and paste the output of:
`sudo -u git -H bundle exec rake gitlab:env:info RAILS_ENV=production`)
</pre>
</details>
#### Results of GitLab application Check
<!-- Input any relevant GitLab application check information if needed. -->
<details>
<summary>Expand for output related to the GitLab application check</summary>
<pre>
(For installations with omnibus-gitlab package run and paste the output of:
`sudo gitlab-rake gitlab:check SANITIZE=true`)
(For installations from source run and paste the output of:
`sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production SANITIZE=true`)
(we will only investigate if the tests are passing)
</pre>
</details>
issue