Run workflow on Windows, macOS and Linux

Author: jonahgraham

.github/workflows/validate.yml

@@ -2,7 +2,11 @@ on: [ pull_request, push]
 
 jobs:
   build:
-    runs-on: ubuntu-latest
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, windows-latest, macos-latest]
     steps:
     - uses: actions/checkout@v3
     - name: Set up JDK 11 ☕