CI: Moose 12 + simplifications of workflow file

.github/workflows/tests.yml

@@ -1,31 +1,19 @@
-name: MoosePy tests
+name: Tests
 
 env:
   GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
 
-on:
-  push:
-    branches:
-      - dev
-      - master
-  pull_request:
-    branches:
-      - dev
-      - master
-  workflow_dispatch:
-
+on: [ push, pull_request, workflow_dispatch ]
+
 jobs:
   build:
-    strategy:
-      matrix:
-        platform: [ubuntu-latest, macos-latest ]
-    runs-on: ${{ matrix.platform }}
+    runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v3
       - uses: hpi-swa/setup-smalltalkCI@v1
         id: smalltalkci
         with:
-          smalltalk-image: Moose64-11
+          smalltalk-image: Moose64-12
       - run: smalltalkci -s ${{ steps.smalltalkci.outputs.smalltalk-image }}
         shell: bash
         timeout-minutes: 15