"qemu -display spice-app" fails due to missed spice+unix schema in remote-viewer.desktop

[Max]

Try the following command (optionally add -cdrom ubuntu.iso):
    qemu-system-x86_64 -display spice-app
Actual result:
    qemu-system-x86_64: info: Launching display with URI: spice+unix:///tmp/.XXGMF1/spice.sock
    qemu-system-x86_64: Failed to launch spice+unix:///tmp/.XXGMF1/spice.sock URI: The specified location is not supported
    qemu-system-x86_64: You need a capable Spice client, such as virt-viewer 8.0
Expected result:
    no such error, with additional arguments VM is started.

Actually virt-viewer-7.0 (20.04 focal - 21.10 impish) supports spice+unix scheme
but it is not specified in remote-viewer.desktop.

Upstream commit fixing this issue is included since v8.0 tag:

https://gitlab.com/virt-viewer/virt-viewer/-/commit/c4f6142f15c4e51cbf427f5f1bf1fc6ac0e10d88
remote-viewer: add handling of spice+unix and spice+tls schemes
2018-07-27T15:12:00Z

Accordingly to https://virt-manager.org/download/
virt-viewer 11.0 is available since Friday November 18th, 2021

I hope, the best way to fix the issue is to package new version,
however I have not tried to build it, so some complications may exist.

Workaround:
Add to ~/.config/mimeapps.list
---- >8 ----
[Added Associations]
x-scheme-handler/spice+unix=remote-viewer.desktop
---- 8< ----

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.