auto-retry binary builds on runner system failure

Try to work around broken build results because runners go away.

debian/.debian-ci.yml

@@ -78,6 +78,9 @@ default:
     - apt-get install sudo
     - apt-get install build-essential devscripts reprepro fakeroot
   image: ${DOCKER_ARCH}/${OS}:${SUITE}${IMAGE_EXTENSION}
+  retry:
+    max: 2
+    when: runner_system_failure
 
   script:
     - 'echo "SUITE: $SUITE"'