fix(ci): Stop running changelog-check.yml on merge_group trigger (#923)

Removes the `merge_group` trigger from the changelog workflow in CI,
which the action is not configured to support and will cause it to fail.

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Low risk workflow change limited to CI triggers; it only reduces when
the job runs and should not affect runtime code.
> 
> **Overview**
> Stops `.github/workflows/changelog-check.yml` from running on the
`merge_group` event, leaving it triggered only by `pull_request`
activity.
> 
> This avoids running the changelog check action in a context it isn’t
configured to handle (merge queue), preventing CI failures there.
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
55737d8. Bugbot is set up for automated
code reviews on this repo. Configure
[here](https://www.cursor.com/dashboard/bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: rekmarks

.github/workflows/changelog-check.yml

@@ -3,7 +3,6 @@ name: Check Changelog
 on:
   pull_request:
     types: [opened, synchronize, labeled, unlabeled]
-  merge_group:
 
 jobs:
   check-changelog: