ci: update actions/checkout to v3

Author: umarcor

.github/workflows/build.yml

@@ -21,7 +21,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
 
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v3
 
     - name: Build
       run: ./build.sh "${{ matrix.file }}.dockerfile"