🐍 Ensure support for Python 3.12/3.8/3.7

The README claims that Python 3.7 or higher is required,
so I believe it would be nice to ensure that all 3.7+
versions are actually supported by enabling testing
against them on CI.

These changes also:
  - add coverage reporting
  - disable fail-fast mode for tests
  - make CI use pipx to install poetry
  - make CI use pytest to run tests
  - force colors on CI
  - bump actions/checkout to v4
  - bump actions/setup-python to v5

.github/workflows/codeql-analysis.yml

@@ -16,7 +16,7 @@ jobs:
 
     steps:
     - name: Checkout repository
-      uses: actions/checkout@v2
+      uses: actions/checkout@v4
       with:
         # We must fetch at least the immediate parents so that if this is
         # a pull request then we can check out the head.

.github/workflows/test.yml

@@ -14,22 +14,34 @@ on:
       - ".github/workflows/test.yml"
       - "**.py"
 
+env:
+  FORCE_COLOR: '1'
+
 jobs:
   test:
     strategy:
+      fail-fast: false
       matrix:
-        python: ["3.9", "3.10", "3.11"]
+        python:
+          - "3.12"
+          - "3.11"
+          - "3.10"
+          - "3.9"
+          - "3.8"
+          - "3.7"
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
-      - uses: actions/setup-python@v4
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
         with:
           python-version: ${{ matrix.python }}
       - name: Setup Graphviz
         uses: ts-graphviz/setup-graphviz@v1
       - name: Install poetry
-        run: curl -sSL https://install.python-poetry.org | python3 -
-      - name: Run all tests
         run: |
-          poetry install
-          poetry run python -m unittest -v tests/*.py
+          pipx install poetry
+          poetry env use ${{ matrix.python }}
+      - name: Install dependencies
+        run: poetry install
+      - name: Run all tests
+        run: poetry run pytest