deb: DEBIAN_FRONTEND=noninteractive is ENV not ARG

It would be bad to preserve this as and env, so just
apply it per apt-get install, or in debian.Dockerfile
since there are so many, add it to the beginning of the
build step.

ci_build_images/debian-release.Dockerfile

@@ -7,14 +7,11 @@ ARG BASE_IMAGE
 FROM "$BASE_IMAGE"
 LABEL maintainer="MariaDB Buildbot maintainers"
 
-# This will make apt-get install without question
-ARG DEBIAN_FRONTEND=noninteractive
-
 # Install updates and required packages
 RUN . /etc/os-release; \
     apt-get update \
     && apt-get -y upgrade \
-    && apt-get -y install --no-install-recommends \
+    && DEBIAN_FRONTEND=noninteractive apt-get -y install --no-install-recommends \
     aptly \
     buildbot-worker \
     ca-certificates \

ci_build_images/debian.Dockerfile

@@ -9,9 +9,6 @@ ARG MARIADB_BRANCH=11.1
 LABEL maintainer="MariaDB Buildbot maintainers"
 ENV CARGO_NET_GIT_FETCH_WITH_CLI=true
 
-# This will make apt-get install without question
-ARG DEBIAN_FRONTEND=noninteractive
-
 # Enable apt sources
 RUN . /etc/os-release \
     && if [ -f "/etc/apt/sources.list.d/$ID.sources" ]; then \
@@ -26,6 +23,7 @@ RUN . /etc/os-release \
 # Install updates and required packages
 # see: https://cryptography.io/en/latest/installation/
 RUN . /etc/os-release \
+    && export DEBIAN_FRONTEND=noninteractive \
     && apt-get update \
     && apt-get -y upgrade \
     && apt-get -y install --no-install-recommends \