Convert the problem to failure to install perl:s390x

    The following packages have unmet dependencies:
     perl : Conflicts: perl:s390x but 5.22.1-9ubuntu0.9 is to be installed
     perl:s390x : Depends: perl-base:s390x (= 5.22.1-9ubuntu0.9) but it is not going to be installed
                  Depends: libperl5.22:s390x (= 5.22.1-9ubuntu0.9) but it is not going to be installed
                  Conflicts: perl but 5.22.1-9ubuntu0.9 is to be installed

Author: EliahKagan

etc/docker/Dockerfile.test-cross

@@ -14,7 +14,11 @@ RUN set -uC && \
     apt-get install --no-install-recommends -y software-properties-common && \
     add-apt-repository -y ppa:git-core/ppa && \
     apt-get update && \
-    apt-get install --no-install-recommends -y "git$apt_suffix" jq patch && \
+    apt-get install --no-install-recommends -y "libc6$apt_suffix" "libcurl3-gnutls$apt_suffix" \
+        "libexpat1$apt_suffix" "libpcre2-8-0$apt_suffix" "zlib1g$apt_suffix" "perl$apt_suffix" \
+        liberror-perl git-man patch jq && \
+    apt-get download "git$apt_suffix" && \
+    dpkg --ignore-depends="liberror-perl$apt_suffix" -i ./git[-_]*.deb && \
     apt-get purge --autoremove software-properties-common && \
     apt-get clean && \
     rm -rf /var/lib/apt/lists/* && \