Publish arm image too (#21)

base image (https://hub.docker.com/_/docker/tags?page=1&name=20.10-dind) do support amd64 and arm64

so we can do too

Reviewed-on: https://codeberg.org/woodpecker-plugins/plugin-docker-buildx/pulls/21

.gitignore

@@ -1,5 +1,6 @@
 /release/
-/drone-docker-buildx*
+
+docker-buildx
 
 coverage.out
 CHANGELOG.md