Use latest version of Poetry

Author: benedikt

.github/workflows/test.yml

@@ -24,7 +24,7 @@ jobs:
       - name: Install Poetry
         uses: snok/install-poetry@v1
         with:
-          version: 1.5.1
+          version: 2.1.1
           virtualenvs-create: true
           virtualenvs-in-project: true