[APT repo] Provide a binary-all/Packages only, no primary arch list

[MichaIng]

Hey guys,

while checking how to best enable riscv64 support for Webmin's own APT 
repository, we recognised that APT falls back to/uses 
"binary-all/Packages" packages, but still complains with a warning if no 
"binary-riscv64/Packages" is present and declared in the Release file of 
the APT repository:
-------
W: Skipping acquire of configured file 'contrib/binary-riscv64/Packages' 
as repository 'https://download.webmin.com/download/repository sarge 
InRelease' does not seem to provide it (sources.list entry misspelt?)
-------
Is this expected behaviour, i.e. is every repository expected to provide 
dedicated package lists for every architecture, or is there a way to 
provide an "all" architectures list only, without causing clients to 
throw warnings? In case of Webmin, all packages are perl scripts, have 
"Architecture: all" declared and naturally support all architectures. So 
it seems unnecessary to provide clones of a single package list for 
every architecture explicitly, and having to do so whenever a new one 
appears.

--
Best regards,

Micha