Fix unset ARCH option

Author: vmcj

.github/jobs/chroot_checks.sh

@@ -3,7 +3,9 @@
 . .github/jobs/ci_settings.sh
 
 if [ -n "$1" ] && [ "$1" != "default" ]; then
-export ARCH="$1"
+    export ARCH_OPTION="-a $1"
+else
+    export ARCH_OPTION=""
 fi
 
 function finish() {
@@ -46,7 +48,7 @@ cd /opt/domjudge/judgehost/bin || exit 1
 section_end chroot
 
 section_start "Show minimal chroot"
-./dj_make_chroot -a "$ARCH" | tee -a "$ARTIFACTS"/chroot.log
+./dj_make_chroot "$ARCH_OPTION" | tee -a "$ARTIFACTS"/chroot.log
 section_end
 
 section_start "Test chroot contents"