site-admin repo page: overflow: auto instead of scroll

Created by: mrnugget

I know I suggested this in the last PR, but turns out I was wrong (huh). This does look better.

Before there was always this padding on the right that looked off:

Now it only shows up when there needs to be a scrollbar:

Test plan

• Manual testing

App preview:

• Web
• Storybook

Check out the client app preview documentation to learn more.