On riscv64, trying to install unoconv results in a failure because this architecture does not have libreoffice package (see below). Given the strong dependency of unoconv with python3-uno (which is part of libreoffice package), adding a build dependency would fix that problem by not building unoconv for riscv64.
root@ubuntu:~# apt install unoconv
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:
The following packages have unmet dependencies:
unoconv : Depends: python3-uno (>= 4.0) but it is not installable
Recommends: libreoffice-writer but it is not installable
Recommends: libreoffice-draw but it is not installable
Recommends: libreoffice-calc but it is not installable
Recommends: libreoffice-impress but it is not installable
E: Unable to correct problems, you have held broken packages.
root@ubuntu:~# apt install python3-uno
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Package python3-uno is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
E: Package 'python3-uno' has no installation candidate
I attach a new patch that I cleaned from trailing spaces.
I re-tested it locally on jammy and it fails to build because of the new dependency as expected.