BF: add CI to run flake8

Workflow file existed before, but was never triggered.

.github/workflows/main.yml

@@ -1,34 +1,33 @@
-# This is a basic workflow to help you get started with Actions
+name: tests
 
-name: prometheus_fzj_weather_exporter tests
-
-# Controls when the workflow will run
 on:
-  # Triggers the workflow on push or pull request events but only for the main branch
   push:
-    branches: [ main ]
+    branches:
+      - main
   pull_request:
-    branches: [ main ]
 
 jobs:
   build:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: ['3.6', '3.7', '3.8', '3.9', '3.10', 'pypy3']
-
+        # 3.6 is minimal version of setup.py, 3.12 currently the newest
+        python-version: ['3.6', '3.12']
+
     steps:
     - uses: actions/checkout@v3
-
+    - name: Set up Python ${{ matrix.python-version }}
+      uses: actions/setup-python@v4
+      with:
+        python-version: ${{ matrix.python-version }}
     - name: git config
       run: |
-        git config --global user.email "you@example.com"
-        git config --global user.name "Your Name"
-
+        git config --global user.email "weather@exporter.com"
+        git config --global user.name "Weather Exporter"
     - name: Install dependencies
       run: |
+        pip install .
         pip install flake8
-        
     - name: flake8 linting
       run: |
-        flake8 $(find . -type f -name "*.py")
+        flake8