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.

[gijsk]

(We may also wish to alter the wording as different items are available on different channels but the page as a whole is available on release.)

[janbrasna]

@gijsk Do you have any other wording updates you'd like to include?

Any change to this string will go to the l10n community triggering new translations, so if you'd like to see any other tweaks to the string, it's sensible to push them all in one changeset.