nginx-golang-mysql: code review fixes

Co-authored-by: Guillaume Lours <guillaume@lours.me>
Signed-off-by: Milas Bowman <milas.bowman@docker.com>

nginx-golang-mysql/.docker/docker-compose.yaml

@@ -2,7 +2,7 @@ services:
   backend:
     build:
       context: backend
-      target: builder
+      target: dev-envs
     volumes:
       - /var/run/docker.sock:/var/run/docker.sock
     secrets:

nginx-golang-mysql/backend/Dockerfile

@@ -19,7 +19,7 @@ RUN --mount=type=cache,target=/go/pkg/mod/cache \
 
 CMD ["/code/bin/backend"]
 
-FROM builder as dev-envs
+FROM builder AS dev-envs
 
 RUN <<EOF
 apk update