"next" in Customizer menu section should be capital

[hardeepasrani]

When you start creating a new menu from the Customizer, it has this text: "Click "next" to start adding links to your new menu."

The button label is Next, so it should also be Next in quotes instead of next, just like it is everywhere else in similar cases. Screenshot and patch attached.

[hardeepasrani]

Screenshot of Appearance > Menu

[hardeepasrani]

First patch.

[melchoyce]

In 41954:

Customize Menus: Update capitalization of "next" to match case on the "Next" button.

Props hardeepasrani.
Fixes #42287.