slight rendering errors when there are no matching repos

[bpmct]

noticed two small things on the default dark theme

1. helper text is unreadable with highlight
2. can we move "► Why am I seeing all workspaces?" to below the

   ---

   instead of overlapping it?

https://github.com/coder/backstage-plugins/assets/22407953/02f70991-9895-436d-8bf3-7320e461f041

[Parkreiner]

On it