Update system packages when building Docker image to avoid picking up upstream vulnerabilities (#8752)

Author: joehan

scripts/publish/firebase-docker-image/Dockerfile

@@ -2,6 +2,8 @@ FROM node:lts-alpine AS app-env
 
 # Install Python and Java and pre-cache emulator dependencies.
 RUN apk add --no-cache python3 py3-pip openjdk11-jre bash && \
+    apk update && \
+    apk upgrade && \
     npm install -g firebase-tools && \
     firebase setup:emulators:database && \
     firebase setup:emulators:firestore && \