Fix build, cherry-pick commit to build on arm, update depends, and update theme-switcher

[ids1024]

It seems https://github.com/pop-os/desktop-widget/pull/58 and https://github.com/pop-os/desktop-widget/pull/59 conflicted, breaking the build. This fixes that. It also update dependencies and doesn't reference non-existent branches. Superseding https://github.com/pop-os/desktop-widget/pull/67 and fixing https://github.com/pop-os/desktop-widget/issues/68.

We haven't ended up really changing anything here in impish, so having separate branches complicates things. So my plan is to delete master_impish, add placeholder bionic and focal branches, and rename master_hirsute to just master. So I've cherry-picked the commit to build on arm from master_impish.

This has a commit to test the change from https://github.com/pop-os/theme-switcher/pull/29.

Test but DO NOT merge. When https://github.com/pop-os/theme-switcher/pull/29 is merged, the last commit should be removed and cargo update should be run again. (Plus the branch changes.)