chore: run checks for merge queue (#29)

# Motivation

Merge queue entries are not starting required checks because the test
workflow does not listen for GitHub's merge queue event.

# Summary of Changes

- Adds the `merge_group` trigger to the `Test` workflow.
- Leaves the release workflow unchanged so it only runs after pushes to
`main`.

# Testing

- `git diff --check`
- `mise run fmt:check`

# Dependencies/Special Considerations

Existing merge queue entries may need to be re-queued after this PR
lands so GitHub creates new merge-group refs with the updated workflow.

Author: dkarter

.github/workflows/test.yml

@@ -4,6 +4,7 @@ on:
   push:
     branches: [main]
   pull_request:
+  merge_group:
   workflow_dispatch:
 
 jobs: