batches: prevent layout shift on workspace step tabs

Created by: courier-new

Uses the trick we use elsewhere with an ::after element that renders the same contents of the tab but bolder to prevent the layout shift that normally happens when you click the tab and it turns bold.

Before	After

Test plan

Tested locally, as shown in video recordings above.

App preview:

• Web
• Storybook

Check out the client app preview documentation to learn more.