Extend checks for more Python-s

Add a matrix in order to check at least:

- oldest Python version
- default Python version on pkgsrc-current
- newest Python version

Related to #49 and #71.

.github/workflows/python.yml

@@ -12,13 +12,16 @@ jobs:
   build:
     name: Check and test transferwee
     runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        version: ['3.8', '3.10', 3.12']
     steps:
       - name: Checkout code
         uses: actions/checkout@v3
-      - name: Set up Python 3.10
+      - name: Set up Python ${{ matrix.version }}
         uses: actions/setup-python@v4
         with:
-          python-version: '3.10'
+          python-version: ${{ matrix.version }}
       - name: Cache pip
         uses: actions/cache@v3
         with: