reproducible Archlinux: use bpo kernel everywhere to support building latest stuff

Signed-off-by: Holger Levsen <holger@layer-acht.org>

update_jdn.sh

@@ -500,7 +500,7 @@ if [ -f /etc/debian_version ] ; then
 			sudo apt install linux-image-amd64:amd64
 		elif [ "$HOSTNAME" = "osuosl-build169-amd64" ] || [ "$HOSTNAME" = "osuosl-build170-amd64" ] ; then
 			# Arch Linux builds latest stuff which sometimes (eg, currentlt Qt) needs newer kernel to build...
-			#sudo apt install linux-image-amd64/stretch-backports || true # backport kernels are frequently uninstallable...
+			sudo apt install linux-image-amd64/buster-backports || true # backport kernels are frequently uninstallable...
 			:
 		fi
 		# don't (re-)install pbuilder if it's on hold