bump buildx and golang (#58)

- use golang v1.20
- use buildx v0.10.4
  (to have buildkit v0.11.2)

Reviewed-on: https://codeberg.org/woodpecker-plugins/docker-buildx/pulls/58
Reviewed-by: Lauris BH <lafriks@noreply.codeberg.org>
Co-authored-by: 6543 <6543@obermui.de>
Co-committed-by: 6543 <6543@obermui.de>

Dockerfile.multiarch

@@ -1,6 +1,6 @@
-ARG BUILDX_VERSION=0.9.1
+ARG BUILDX_VERSION=0.10.4
 ARG DOCKER_VERSION=20.10-dind
-ARG GOLANG_VERSION=1.18
+ARG GOLANG_VERSION=1.20
 
 FROM --platform=$BUILDPLATFORM golang:${GOLANG_VERSION} as build