Remove 386 from Docker Builds for Ubuntu 20.04

Ubuntu 20.04 no-longer includes 386 binary support.

* Remove 386 from Docker builds

Signed-off-by: Daniel Llewellyn <daniel@snapcraft.ninja>

.github/workflows/build-container-and-wsl.yaml

@@ -32,7 +32,7 @@ jobs:
       uses: docker/build-push-action@v2
       with:
         file: ./portable.Dockerfile
-        platforms: linux/amd64,linux/386
+        platforms: linux/amd64
         push: true
         load: true # Copy to the host's docker daemon so we can use it for WSL export
         tags: ${{ steps.docker_meta.outputs.tags }}