help with watch file and upstream signature

[Lorenzo <plorenzo@disroot.org>]

Hello Mentors,

upstream runit has both the tar.gz and the signature file at

https://smarden.org/runit/install

I would like to check the signature with uscan/gbp import-orig;
the signature file has a different name from the tar archive,
examples that I found (adding .asc to the tar archive name) are not
working.
I'm playing with the pgpsigurlmangle option trying to replace the tar
with 'sha256sum.asc' but no luck so far and I'm not sure it can work
that way.
How can I tell uscan to look for a different filename for the signature?

cat ./debian/watch (not working)
version=4
opts=pgpsigurlmangle=s/runit-([.0-9]+)\.tar\.gz/sha256sum\.asc/  \
https://smarden.org/runit/install.html runit-([.0-9]+)\.tar\.gz

Lorenzo