.github/workflows: update GitHub Action workflow

We can use Poetry directly rather than installing deps with pip.

.github/workflows/python-app.yml

@@ -28,23 +28,19 @@ jobs:
 
     steps:
     - uses: actions/checkout@v3
-    - name: Set up Python 3.10
-      uses: actions/setup-python@v4
+    - name: Install poetry
+      run: pipx install poetry
+    - uses: actions/setup-python@v4
       with:
         python-version: '3.10'
-        cache: 'pip'
-    - name: Install dependencies
-      run: |
-        python -m pip install --upgrade pip
-        pip install flake8 pytest
-        if [ -f requirements.txt ]; then pip install -r requirements.txt; fi
-        if [ -f requirements-dev.txt ]; then pip install -r requirements-dev.txt; fi
+        cache: 'poetry'
+    - run: poetry install
     - name: Lint with flake8
       run: |
         # stop the build if there are Python syntax errors or undefined names
-        flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics
+        poetry run flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics
         # exit-zero treats all errors as warnings. The GitHub editor is 127 chars wide
-        flake8 . --count --exit-zero --max-complexity=10 --max-line-length=127 --statistics
+        poetry run flake8 . --count --exit-zero --max-complexity=10 --max-line-length=127 --statistics
     - name: Set up PostgreSQL
       run: |
         pg_isready -U postgres -d dspacestatistics
@@ -56,7 +52,7 @@ jobs:
         PGPASSWORD: postgres
     - name: Test with pytest
       run: |
-        pytest
+        poetry run pytest
       env:
         PGHOST: localhost
         PGPASSWORD: dspacestatistics