参照下面的指导，单机升级成功，命令总结如下，其他机器升级方便直接拷贝：
pve7to8
pve7to8 --full
apt dist-upgrade
pveversion
#make sure that the system is using the latest Proxmox VE 7.4 packages
sed -i 's/bullseye/bookworm/g' /etc/apt/sources.list
sed -i -e 's/bullseye/bookworm/g' /etc/apt/sources.list.d/pve-install-repo.list
sed -i -e 's/bullseye/bookworm/g' /etc/apt/sources.list.d/pve-no-subscription.list
echo "deb https://mirrors.ustc.edu.cn/proxmox/debian/ceph-quincy bookworm main" > /etc/apt/sources.list.d/ceph.list
apt update
apt dist-upgrade
拷贝命令后在SHELL中粘贴回车执行就行
