Add matrix strategy

Author: Vahila

.github/workflows/main.yml

@@ -2,8 +2,11 @@ name: using mpm to install MATLAB
 on: push
 jobs:
   my-job:
+    strategy:
+      matrix:
+        os: [ubuntu-latest, windows-latest, macos-latest]
     name: Run System tests
-    runs-on: [ubuntu-latest, windows-latest, macos-latest]
+    runs-on: ${{ matrix.os }}
     steps:
       - name: Check out repository
         uses: actions/checkout@v2