[BUGFIX] Page module: fix bottom margin of language header

Add missing `bottom-margin` by only overriding `margin-top`
of generic `h2` style.

Resolves: #79699
Releases: master
Change-Id: I9dc274305694aef3c526c3a342d7b994765094ec
Reviewed-on: https://review.typo3.org/51597


Tested-by: TYPO3com <no-reply@typo3.com>
Tested-by: Riccardo De Contardi <erredeco@gmail.com>
Reviewed-by: Michael Oehlhof <typo3@oehlhof.de>
Tested-by: Michael Oehlhof <typo3@oehlhof.de>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>