fix: re-state arg from env in Dockerfile

Dockerfile

@@ -14,6 +14,9 @@ WORKDIR /app
 RUN apk update --no-cache
 RUN apk add --no-cache build-base gcc curl git wget nodejs npm
 
+ARG MIX_ENV=prod
+ENV MIX_ENV=$MIX_ENV
+
 # install hex + rebar
 RUN mix local.hex --force && \
     mix local.rebar --force
@@ -26,7 +29,7 @@ RUN mkdir config
 # copy compile-time config files before we compile dependencies
 # to ensure any relevant config change will trigger the dependencies
 # to be re-compiled.
-COPY config/config.exs config/${MIX_ENV}.exs config/
+COPY config/config.exs config/$MIX_ENV.exs config/
 RUN mix deps.compile
 
 COPY priv priv
@@ -58,6 +61,9 @@ RUN apk update --no-cache
 RUN apk add --no-cache tzdata openssl ncurses wget
 RUN apk add --no-cache chromium --repository=http://dl-cdn.alpinelinux.org/alpine/v3.18/community
 
+ARG MIX_ENV=prod
+ENV MIX_ENV=$MIX_ENV
+
 ENV LANG en_US.UTF-8
 ENV LANGUAGE en_US:en
 ENV LC_ALL en_US.UTF-8
@@ -69,7 +75,7 @@ RUN chown nobody /app
 ENV MIX_ENV="prod"
 
 # Only copy the final release from the build stage
-COPY --from=builder --chown=nobody:root /app/_build/${MIX_ENV}/rel/pescarte ./
+COPY --from=builder --chown=nobody:root /app/_build/$MIX_ENV/rel/pescarte ./
 
 USER nobody