[SG-35478] Branch/Tag/Commit + Repositories selector: Modals have no `title`

Created by: gitstart-sourcegraph

Description

• Added aria-labelled by to change revision popover to add title to the modal
• Added aria-labelled by to change repository popover to add title to the modal

Refs

Sourcegraph Issue GitStart Issue

Test plan

• Navigate to the Branch/Tag/Commit + Repositories selector page e.g /github.com/sourcegraph/sourcegraph and run ARC toolkit with the change revision or change repository modal open

Loom Link

• https://www.loom.com/share/a95f8dac35f64e4cb1b926f3c667972c

App preview:

• Web
• Storybook

Check out the client app preview documentation to learn more.