update build boilerplate (thanks GitHub)

Author: joonas-fi

.github/workflows/build.yml

@@ -6,7 +6,7 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v3
 
     - uses: docker/setup-buildx-action@v1