ci: use tox within poetry env

Author: boriel

.github/workflows/python-app.yml

@@ -30,7 +30,7 @@ jobs:
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
-        pip install poetry tox
+        pip install poetry
         poetry install
     - name: Cache tox environments
       id: cache-tox
@@ -42,6 +42,5 @@ jobs:
         # only takes a single file path or pattern at the moment.
         key: ${{ runner.os }}-${{ matrix.python }}-tox-${{ hashFiles('setup.cfg') }}-${{ hashFiles('pyproject.toml') }}
 
-
     - name: Run Tox
-      run: tox -- --no-cov
+      run: poetry run tox -- --no-cov