Update GitHub actions to use Node 16

https://github.blog/changelog/2022-09-22-github-actions-all-actions-will-begin-running-on-node16-instead-of-node12/

Author: th-otto

.github/workflows/build.yml

@@ -10,7 +10,7 @@ jobs:
   build:
     runs-on: ubuntu-20.04
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - name: Install SSH keys
         if: ${{ github.event_name == 'push' }}
         env: