Add python matrix to test workflow

Author: bnavigator

.github/workflows/build.yml

@@ -35,6 +35,9 @@ jobs:
   test:
     runs-on: ubuntu-latest
     timeout-minutes: 20
+    matrix:
+      # used by the jupyterlab/maintainer-tools base-setup action
+      python-version: ['3.8', '3.9', '3.10', '3.11', '3.12']
     steps:
     - name: Checkout
       uses: actions/checkout@v3