Stop using windows-2016 since it's gone

Author: Jaykul

.github/workflows/build.yml

@@ -56,7 +56,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [windows-2016, windows-latest, ubuntu-latest, macos-latest]
+        os: [windows-latest, ubuntu-latest, macos-latest]
     steps:
     - name: Download Build Output
       uses: actions/download-artifact@v2