Replace AppVeyor testing with GH Actions

.github/workflows/testing.yml

@@ -13,10 +13,15 @@ on:
 jobs:
   build:
 
-    runs-on: ubuntu-22.04
+    runs-on: ${{ matrix.os }}
+
     strategy:
       matrix:
+        os: [ubuntu-latest, windows-latest]
         python-version: ["3.8", "3.9", "3.10", "3.11", "3.12"]
+        exclude:
+          - os: windows-latest # only test with Python 3.10 on Windows
+            python-version: ["3.8", "3.9", "3.11", "3.12"]
 
     steps:
     - uses: actions/checkout@v4