coverage.sh: host architecture in --logfile output must depend on host

coverage.sh

@@ -1948,7 +1948,7 @@ export LC_ALL=C.UTF-8
 $CMD --mode=root --variant=apt --logfile=log $DEFAULT_DIST /tmp/debian-chroot $mirror
 # we check the full log to also prevent debug printfs to accidentally make it into a commit
 cat << LOG | diff - log
-I: chroot architecture amd64 is equal to the host's architecture
+I: chroot architecture $HOSTARCH is equal to the host's architecture
 I: running apt-get update...
 I: downloading packages with apt...
 I: extracting archives...