How to attach more than 25 volumes to a guest

Issue

• Attempting to add more than 25 or 26 volumes (number depends on whether the VM was booted from volume) to a server fails with the following error:

  2023-01-13 16:48:56.051 7 ERROR nova.virt.block_device [instance: 07120906-e3ea-4100-9f96-7180e20a1c62] libvirt.libvirtError: internal error: No more available PCI slots
  2023-01-13 16:48:56.051 7 ERROR nova.virt.block_device [instance: 07120906-e3ea-4100-9f96-7180e20a1c62]
  2023-01-13 16:48:59.260 7 ERROR nova.compute.manager [req-432b58ba-edda-4bf3-906b-e6d11070a196 ae7c2e975f91433cb47a08651fd2a91f ab83426af6b04f818ddc0b2615e9afe5 - default default] [instance: 07120906-e3ea-4100-9f96-7180e20a1c62] Failed to attach 4c799126-aaa7-49e3-be8b-f4590241ffe9 at /dev/vdaa: libvirt.libvirtError: internal error: No more available PCI slots