shell-completion: add tdx to systemd-vmspawn --coco values

Missed in a78afc1616 ("vmspawn: add Intel TDX confidential VM
support")

Signed-off-by: Paul Meyer <katexochen0@gmail.com>

shell-completion/bash/systemd-vmspawn

@@ -70,7 +70,7 @@ _systemd_vmspawn() {
     elif __contains_word "$prev" ${OPTS[IMAGE_DISK_TYPE]}; then
         comps='virtio-blk virtio-scsi nvme'
     elif __contains_word "$prev" ${OPTS[COCO]}; then
-        comps='no sev-snp'
+        comps='no sev-snp tdx'
     elif __contains_word "$prev" ${OPTS[ARG]}; then
         comps=''
     else