Do not use slim Docker image since we need to build pzstd wheel with gcc

Dockerfile

@@ -1,6 +1,6 @@
 FROM redis:6.2.4-buster AS redis
 
-FROM python:3.8-slim-buster
+FROM python:3.8-buster
 
 RUN groupadd -r -g 999 redis && useradd -r -g redis -u 999 redis
 COPY --from=redis /usr/local/bin/redis-server /usr/local/bin/redis-server