Link to working XenCenter snapshot documentation from article on upgrading GitHub Enterprise Server (#18970)

Co-authored-by: Lucas Costi <lucascosti@users.noreply.github.com>

Author: mattpollard

content/admin/enterprise-management/upgrading-github-enterprise-server.md

@@ -81,7 +81,7 @@ There are two types of snapshots:
 | Hyper-V | VM | <https://docs.microsoft.com/windows-server/virtualization/hyper-v/manage/enable-or-disable-checkpoints-in-hyper-v>
 | Google Compute Engine | Disk | <https://cloud.google.com/compute/docs/disks/create-snapshots>
 | VMware | VM | <https://pubs.vmware.com/vsphere-50/topic/com.vmware.wssdk.pg.doc_50/PG_Ch11_VM_Manage.13.3.html>
-| XenServer | VM | <https://support.citrix.com/article/CTX122978>
+| XenServer | VM | <https://docs.citrix.com/en-us/xencenter/current-release/vms-snapshots.html>
 
 ### Upgrading with a hotpatch