Remove merge_group trigger from CodeQL workflow (#3512)

CodeQL analysis fails on `merge_group` events. Removed this trigger from
the workflow configuration.

## Changes
- Removed `merge_group` event trigger from
`.github/workflows/codeql-analysis.yml`
- CodeQL now runs only on push to main, pull requests, and scheduled
runs

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<!-- CURSOR_SUMMARY -->
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> [!NOTE]
> **Low Risk**
> Workflow trigger-only change; it reduces when CodeQL runs but does not
affect application/runtime code.
> 
> **Overview**
> Removes the `merge_group` event trigger from the `CodeQL Analysis`
GitHub Actions workflow, so CodeQL no longer runs for merge-queue
events.
> 
> CodeQL will now run only on pushes to `main`, pull requests targeting
`main`, and the scheduled nightly cron job.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
4808ec4. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: callicles <4429209+callicles@users.noreply.github.com>

Author: Copilot

.github/workflows/codeql-analysis.yml

@@ -5,8 +5,6 @@ on:
     branches: [main]
   pull_request:
     branches: [main]
-  merge_group:
-    types: [checks_requested]
   schedule:
     - cron: "0 0 * * *"