Bring back the matrix

Author: pamelafox

.github/workflows/app-tests.yaml

@@ -33,8 +33,8 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: ["ubuntu-latest"]
-        python_version: ["3.10"]
+        os: ["ubuntu-latest", "windows-latest", "macos-latest-xlarge", "macos-13"]
+        python_version: ["3.10", "3.11", "3.12"]
         exclude:
           - os: macos-latest-xlarge
             python_version: "3.10"