When I leave the default entry

```
("gnu" . "https://elpa.gnu.org/packages/")
```

in `package-archives`, I get the error described here:

https://emacs.stackexchange.com/questions/58424/is-elpa-broken

However, when  I change the ELPA URL scheme to just `http`,
everything works fine, including signature verification.
Therefore I can see GPG signatures have nothing to do with this,
despite my earlier follow-up to #942413.

I think the answer I got on the stackexchange question might well
be spot on. It points me to:

https://debbugs.gnu.org/cgi/bugreport.cgi?bug=34341#46

which may be a good thing to backport to Debian's 26.1