Specify platform and use buildx

Author: testillano

.github/workflows/ci.yml

@@ -65,6 +65,9 @@ jobs:
         password: ${{ secrets.GITHUB_TOKEN }}
         # logout at job end:
         logout: true
+    -
+      name: Set up Docker Buildx
+      uses: docker/setup-buildx-action@v2
     -
       name: Build (but not push) builder image
       id: docker_build1
@@ -74,7 +77,9 @@ jobs:
         file: Dockerfile.build
         build-args: base_os=ubuntu
         context: .
+        platforms: linux/amd64
         #push: true
+        load: true
     -
       name: Image digest
       run: echo ${{ steps.docker_build1.outputs.digest }}
@@ -87,7 +92,9 @@ jobs:
         file: Dockerfile
         build-args: base_tag=local
         context: .
+        platforms: linux/amd64
         #push: true
+        load: true
     -
       name: Image2 digest
       run: echo ${{ steps.docker_build2.outputs.digest }}