vagrant: backports have moved to archive.debian for buster

vagrant-env/kadeploy_provision.sh

@@ -6,6 +6,8 @@ install_package() {
 wget http://packages.grid5000.fr/grid5000-archive-key.asc -q -O- | apt-key add -
 echo deb http://packages.grid5000.fr/deb/g5k-postinstall/ ./ > /etc/apt/sources.list.d/postinstall.list
 echo deb http://packages.grid5000.fr/deb/kadeploy-kernels/ ./ > /etc/apt/sources.list.d/kadeploykernel.list
+
+sed -i '/backports/s|deb.debian.org|archive.debian.org|g' /etc/apt/sources.list
 DEBIAN_FRONTEND=noninteractive apt-get update
 DEBIAN_FRONTEND=noninteractive apt-get install -y ruby rubygems lsb-release git taktuk rake help2man mariadb-server libmariadbclient-dev ruby-dev ident2 syslinux ncat dnsmasq isc-dhcp-server tftpd-hpa pxelinux apache2
 DEBIAN_FRONTEND=noninteractive apt-get install -y g5k-postinstall kadeploy3-deploy-kernel-{buster,bullseye}{,-arm64,-ppc64}