Site config errors disappear immediately

Created by: hopkinscl

• Sourcegraph version: Reproduced on 3.41 and Sourcegraph.com
• Platform information: Reproduced on demo.sourcegraph.com, Sourcegraph.com, and self-hosted customer instance (Kubernetes/AWS EKS)

Steps to reproduce:

1. Navigate to site config
2. Add an unnecessary character (e.g. a duplicate comma or curly brace) and save changes

Expected behavior: Error message will appear until it's dismissed by the user

Actual behavior: Error message flashes on the screen and disappears before it's readable (video here)