Update GH actions for new project packaging

They were trying to read requirements files which no longer exist.

Author: pont-us

.github/workflows/tests.yml

@@ -27,8 +27,7 @@ jobs:
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
-        pip install -r requirements-dev.txt
-        pip install -r requirements.txt
+        pip install .
     - name: Lint with flake8
       run: |
         # stop the build if there are Python syntax errors or undefined names