ci: add darwin

Author: sbinet

.github/workflows/ci.yml

@@ -20,7 +20,7 @@ jobs:
     strategy:
       matrix:
         go-version: [1.17.x, 1.16.x]
-        platform: [ubuntu-latest, windows-latest]
+        platform: [ubuntu-latest, macos-latest, windows-latest]
     runs-on: ${{ matrix.platform }}
     steps:
     - name: Install Go