Fix Build and push complement image CI job not having Poetry for complement.sh (#19578)

❌ `Build and push complement image`,
https://github.com/element-hq/synapse/actions/runs/23176317296/job/67339146082
```
scripts-dev/complement.sh: line 227: poetry: command not found
```

Follow-up to https://github.com/element-hq/synapse/pull/19523

This regressed in https://github.com/element-hq/synapse/pull/19476


### Testing strategy

1. Visit
https://github.com/element-hq/synapse/actions/workflows/push_complement_image.yml
 1. **Run workflow**:
- **Use workflow from:**
`madlittlemods/fix-complement-push-image-ci-job-poetry`
     - **Branch:** `develop`
 1. Wait for CI to run and pass ✅

.github/workflows/push_complement_image.yml

@@ -47,6 +47,10 @@ jobs:
         if: github.event_name == 'push'
         with:
           ref: master
+      # We use `poetry` in `complement.sh`
+      - uses: matrix-org/setup-python-poetry@5bbf6603c5c930615ec8a29f1b5d7d258d905aa4 # v2.0.0
+        with:
+          poetry-version: "2.2.1"
       - name: Login to registry
         uses: docker/login-action@c94ce9fb468520275223c153574b00df6fe4bcc9 # v3.7.0
         with: