--deb-dist option does not set the distribution

[hiddenman]

According to the #1929, --deb-dist must set "distribution".
However, it does not set anything so the changelog file just have an empty value like (as well as control file inside the .deb file (it just does not contain Distribution field at all)

openvpn-otp (1.0-4-g47f8ccf) ; urgency=medium

Checking the sources shows that the distribution is set only if the --deb-generate-changes is set (and it puts Distribution: bookworm in the .changes file): https://github.com/jordansissel/fpm/blob/main/lib/fpm/package/deb.rb#L680

However this is done too late and the changelog is already generated with empty value

[tomberek]

Confirmed and encountered on 1.15.1.