Ensure upgrade targets do not expand beyond installed packages

[razor-x]

Closes #975

Hopefully I understood this correctly:

1. The initial filtered list should be the allowed package names to upgrade based only on what is installed.
2. The next two lists are for getting metadata from FAUR. (This is the part I don't fully understand).
3. Regardless of what happens in step (2), the final list should never contain new package names, so we restrict it to the original set.

Initially, I thought I could just apply the original filter again, but step (2) can still expand to more packages than was is currently installed. If I do just this,

        let names = to_upgrade
            .iter()
            .map(|(old, _)| old.name.as_ref())
            .chain(vcs.iter().map(|p| p.name.as_ref()))
            .filter(|name| env.aur.ignores.contains(*name).not());

        install(fll, &env, Mode::Upgrade, names)?;

then "aura :: AUR packages to upgrade:" shows the ignored package, ttf-ms-win11, while the later "aura :: AUR packages:" will have it filtered out.

Since ignored packaged should not be in "AUR packages to upgrade:" I went with the approach in the PR.

[razor-x]

@fosskers or @saifshahriar any feedback on this approach? 🙏🏻