Run github actions with python versions up to 3.12

Reverted flake8 removal and updated dependencies

Author: tmikuska

.github/workflows/main.yml

@@ -21,7 +21,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: [3.8, 3.9]
+        python-version: [3.8, 3.9, 3.10, 3.11, 3.12]
 
     steps:
       - uses: actions/checkout@v2
@@ -32,7 +32,7 @@ jobs:
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip
-          if [ -f tests/requirements.txt ]; then pip install -r tests/requirements.txt; fi
+          pip install -r tests/requirements.txt
       - name: Lint with flake8
         run: |
           # stop the build if there are Python syntax errors or undefined names