When sorting back edges for dependency 'votes' in the new dependency
resolver, dfaure encountered Perl warnings to the effect of:

    > Argument "5/8" isn't numeric in numeric comparison (<=>) at
    > /kdesrc-build/modules/ksb/DependencyResolver.pm line 776.

This turns out to be because converting an entire hash object into a
scalar value doesn't just return the number of key/value pairs, but
instead returns a string describing metadata about the hash object's
content (see https://perlmaven.com/perl-hash-in-scalar-and-list-context)

While this doesn't actually break sorting due to the way Perl constructs
the string, it does cause warnings about using numeric comparisons on
strings.

Fix by applying `scalar` to just the list of keys in the hash containing
votes, which is just a way to determine the number of keys in the hash.