Add pytest-xdist to run test in parallel

Disable coverage because it's not compatible with parallel execution

.github/workflows/flask.yml

@@ -50,7 +50,7 @@ jobs:
         pip install virtualenv
         virtualenv env
         source env/bin/activate
-        pip install flake8 pytest coverage
+        pip install flake8 pytest pytest-xdist
         pip install -r requirements.txt
 
     - name: Prepare database
@@ -68,11 +68,4 @@ jobs:
     - name: Run Tests
       run: |
         source env/bin/activate
-        coverage run --source='ereuse_devicehub' env/bin/pytest -m mvp --maxfail=5 tests/
-        coverage report --include='ereuse_devicehub/*'
-        coverage xml
-
-    - name: Upload coverage to Codecov
-      uses: codecov/codecov-action@v1
-      with:
-        token: ${{ secrets.CODECOV_TOKEN }}
+        pytest -m mvp --maxfail=5 tests/ -n auto