fix: properly adjust Dockerfile

Author: cyyynthia

docker/app/Dockerfile

@@ -2,8 +2,12 @@ FROM postgres:16.8
 
 ENTRYPOINT []
 
-RUN apk --no-cache add openjdk21
-RUN apk --no-cache add "libxml2>=2.13.4-r5"
+RUN <<EOF
+  set -eux
+  apt -qq update
+  apt -qq -y install temurin-21-jdk libxml2
+  rm -rf /var/lib/apt/lists/*
+EOF
 
 #############
 ### Tolgee  #