switch build on python 3.9

Dockerfile

@@ -1,4 +1,4 @@
-FROM python:3.8-alpine as Build
+FROM python:3.9-alpine as Build
 COPY backend/ /pkg/backend
 RUN apk -U --no-progress upgrade && \
   apk --no-progress add gcc musl-dev && \
@@ -13,7 +13,8 @@ RUN apk -U --no-progress upgrade && \
 
 FROM alpine
 COPY --from=Build /pkg /
-RUN apk --no-progress add py3-gunicorn
+RUN  apk -U --no-progress upgrade && \
+  apk --no-progress add py3-gunicorn
 USER chaineTV
 EXPOSE 5000
 WORKDIR /backend