Nightly update message should refer to Firefox Labs instead of Nightly Experiments

[gijsk]

Description

The message right now is:

nightly-whatsnew-want-to-know-which-v2 = Want to know which platform features you could test on { -brand-name-nightly } and can’t see yet on other { -brand-name-firefox } channels? Then have a look at the <a { $attrs }>Nightly Experiments</a> preferences page.

We renamed Nightly Experiments to Firefox Labs in 130. The whats new page should use the new name.