ci: update Poetry installation method in GitHub Actions workflow

Author: titusz

.github/workflows/test-backend.yaml

@@ -16,7 +16,9 @@ jobs:
       - uses: actions/checkout@v3
 
       - name: Install Poetry
-        run: pipx install poetry==1.2.1
+        uses: abatilo/actions-poetry@v3
+        with:
+          poetry-version: 2.1.1
 
       - uses: actions/setup-python@v4
         with: