fix version generation

Dockerfile

@@ -1,28 +1,20 @@
 FROM --platform=$BUILDPLATFORM golang:1.22.5-alpine3.20 AS build
-
 WORKDIR /app
-
 COPY go.mod go.sum ./
 RUN go mod download && go mod verify
-
 COPY *.go ./
 ARG TARGETOS
 ARG TARGETARCH
+ARG VERSION=version_not_set
 RUN GOOS=$TARGETOS GOARCH=$TARGETARCH go build --tags netgo -ldflags="-w -s -X 'main.version=${VERSION}'" -o /container-hoster .
 
 FROM scratch
-
 LABEL org.opencontainers.image.source=https://github.com/wollomatic/container-hoster
 LABEL org.opencontainers.image.description="A simple 'etc/hosts' file injection tool to resolve names of local Docker containers on the host."
 LABEL org.opencontainers.image.licenses=MIT
 LABEL securitytxt="https://wollomatic.de/.well-known/security.txt"
-
 VOLUME /var/run/docker.sock
 VOLUME /hosts
-
 ENTRYPOINT ["/container-hoster"]
-
 WORKDIR /
-
 COPY --from=build ./container-hoster /container-hoster
-COPY ./README.md /README.md