fix: install poetry for github workflow

.github/workflows/tests.yml

@@ -28,6 +28,9 @@ jobs:
           path: .venv
           key: venv-${{ hashFiles('**/poetry.lock') }}
 
+      - name: Install Poetry
+        run: pip install poetry
+
       - name: Configure Poetry
         run: poetry config virtualenvs.in-project true