Batches: Fix minor accessibility issues

Created by: eseliger

Fixes two of the issues reported when doing my audit for this sprint.

Closes https://github.com/sourcegraph/sourcegraph/issues/34542 Closes https://github.com/sourcegraph/sourcegraph/issues/34532

There's one downside to this, the Tabs implementation doesn't overflow on the nav bar, but I flagged that with FPT.

Test plan

Tested this doesn't affect the functionality and actually fixes the accessibility issues reported.

App preview:

• Web
• Storybook

Check out the client app preview documentation to learn more.