Containerfile: install MOTIS in separate stage, from official image

to benefit from layer caching

related: patrickbr/gtfstidy#23

ci/container/Containerfile

@@ -12,14 +12,16 @@ RUN apt-get update -y && \
 
 RUN wget -qO - https://github.com/motis-project/motis/releases/download/${MOTIS_VERSION}/motis-linux-amd64.tar.bz2 | tar -C /opt/ -jx
 
+FROM ghcr.io/gtfstidy/gtfstidy AS gtfstidy
+
 FROM docker.io/debian:bookworm-slim
 
 ARG USERNAME=transitous
 ARG USER_UID=1000
 ARG USER_GID=$USER_UID
 
 RUN apt-get update -y && \
-    apt-get install -y --no-install-recommends git python3-requests python3-jinja2 golang && \
+    apt-get install -y --no-install-recommends git python3-requests python3-jinja2 && \
     apt-get clean -y && \
     rm -rf /var/lib/apt/lists/* 
 
@@ -29,7 +31,8 @@ RUN \
     chown -R "$USER_UID:$USER_GID" /opt/motis
 ENV PATH=/opt/motis:$PATH
 
-RUN GOBIN=/usr/local/bin/ go install github.com/patrickbr/gtfstidy@latest
+# install gtfstidy from `gtfstidy` stage
+COPY --from=gtfstidy /usr/local/bin/gtfstidy /usr/local/bin/gtfstidy
 
 # Create the user / set user rights
 RUN groupadd --gid $USER_GID $USERNAME && \