Add macos to the matrix build.

Author: brendandburns

.github/workflows/maven.yml

@@ -28,7 +28,7 @@ jobs:
       matrix:
         # Test against the LTS Java versions. TODO: add JDK18 when it becomes available.
         java: [ 8.0.x, 11.0.x, 17.0.x ]
-        os: [ windows-latest, ubuntu-latest ]
+        os: [ macos-latest, windows-latest, ubuntu-latest ]
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v2.4.0