Bump styled-components to v6

[christopherbengtsson]

Some styles are lost when using styled-components v6 with React95, e.g. the :focus and :active styles on the <TreeView /> component.

[tegaki-tegaki]

there's now a PR that should solve this :) #398, you can also use the package i made from my fork (no promises that this fork will be maintained for any duration beyond this one-off change 😅, ideally this change gets merged back upstream)