为什么即使我设置了时区，docker build 仍不断询问我时区？

Question

为什么使用下面的 dockerfile 创建新的 docker 映像一直要求我选择时区？我尝试了该ENV TZ命令的多种变体，但均无济于事。

 => => # Please select the geographic area in which you live. Subsequent configuration
 => => # questions will narrow this down by presenting a list of cities, representing
 => => # the time zones in which they are located.
 => => #   1. Africa   3. Antarctica  5. Arctic  7. Atlantic  9. Indian    11. US
 => => #   2. America  4. Australia   6. Asia    8. Europe    10. Pacific  12. Etc
 => => # Geographic area:

我在apt-get install完成后问这个。

Dockerfile：

FROM ubuntu:20.10

ENV TZ Europe/London

RUN apt-get update \
 && apt-get upgrade -y \
 && apt-get -y install autoconf automake bison bzip2 cmake doxygen diffutils flex g++ gcc git gzip libarchive13 libcurl4 libelf1 libgpgme11 libssl1.1 libtool libusb-dev m4 make libncurses-dev patch pkg-config python3 readline-common subversion tar tcl texinfo unzip wget xz-utils

谢谢！