Remove tw-capitalize from localized article pages

[TheoChevalier]

Hi,

I noticed Wagtail is altering translations in the navbar menu of articles pages by capitalizing it following the English capitalization rules. The example below was taken from https://foundation.mozilla.org/fr/research/library/accelerating-progress-toward-trustworthy-ai/whitepaper/

This capitalization is wrong in French and in most languages outside English. The correct capitalization is the one displayed below Accélérer le développement d’une IA digne de confiance

We need to add a conditional so that tw-capitalize is only added for the English page and removed from the other locales in https://github.com/MozillaFoundation/foundation.mozilla.org/blob/main/network-api/networkapi/wagtailpages/templates/fragments/article_subnav.html#L7

┆Issue is synchronized with this Jira Task

[mmmavis]

@TheoChevalier thanks for catching this!