Try to use Nix in Github actions

.github/workflows/tests.yml

@@ -12,21 +12,17 @@ jobs:
   tests:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
-      - name: Set up Python 3.9
-        uses: actions/setup-python@v2
-        with:
-          python-version: 3.9
-      - name: Install dependencies
+      - uses: actions/checkout@v3
+      - uses: cachix/install-nix-action@v18
+      - name: Enable Nix shell
         run: |
-          python -m pip install --upgrade pip
-          pip install -r requirements/local.txt
+          nix develop
       - 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
+          flake8 . --count --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
+          flake8 . --count --exit-zero --max-complexity=10 --statistics
       - name: Test with pytest
         run: |
-          pytest -nauto --ds=network_inventory.settings.ram_test --nomigrations
+          pytest --ds=network_inventory.settings.ram_test -nauto --nomigrations --cov=.