new ci approach

Dockerfile

@@ -1,5 +1,8 @@
 FROM alpine:3.13 AS builder
 
+ARG UNBOUND_TAG="this_invalid_tag_certainly_does_not_exist"
+ARG UNBOUND_CLONE_URL="https://github.com/NLnetLabs/unbound.git"
+
 RUN \
   apk update && \
   apk add alpine-sdk && \
@@ -10,7 +13,7 @@ RUN \
   apk add libevent-dev && \
   mkdir build && \
   cd build && \
-  git clone https://github.com/NLnetLabs/unbound.git && \
+  git clone --branch ${UNBOUND_TAG} ${UNBOUND_CLONE_URL} && \
   cd unbound && \
   ./configure --with-libnghttp2 --with-libevent --prefix /opt/unbound --sysconfdir /etc && \
   make && \