change testing strategy to work on ubuntu, macos and windows

.github/workflows/python-app.yml

@@ -14,8 +14,11 @@ permissions:
 
 jobs:
   build:
+    strategy:
+      matrix:
+        platform: [ubuntu-latest, macos-latest, windows-latest]
 
-    runs-on: ubuntu-latest
+    runs-on: ${{ matrix.platform }}
 
     steps:
     - uses: actions/checkout@v4
@@ -35,4 +38,4 @@ jobs:
         # stop the build if there are Python syntax errors or undefined names
         poetry run flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics
         # exit-zero treats all errors as warnings. The GitHub editor is 127 chars wide
-        poetry run flake8 . --count --exit-zero --max-complexity=10 --max-line-length=127 --statistics
+        poetry run flake8 . --count --exit-zero --max-complexity=10 --max-line-length=127 --statistics