frontend: "Use with your code host" toast covered by search result container

Created by: mrnugget

• Sourcegraph version: 3.4-rc3
• Platform information: Kubernetes cluster

Steps to reproduce:

1. Don't click away the "Use with your code host" toast that pops up for new users
2. Search for something that produces results

Expected behavior:

The toast is in the foreground

Actual behavior:

Info

Changing the z-index of .toast from 50 to 100 fixes it