VersionHistoryController::loadRevisions() throws when the current content language is not among a revision's translations

Problem/Motivation

VersionHistoryController::loadRevisions() calls $revision->getTranslation($currentLangcode) on every revision when the entity type is translatable. This was added in #3356684 so the revision overview links use the current language.

The call assumes each revision has a translation in the current content language, and that isn't always true. For example, a revision may predate the entity or field becoming translatable, so it exists only in another language. Then getTranslation() throws an InvalidArgumentException ("Invalid translation language ... specified"). The revision history page fails instead of listing the revisions.

Steps to reproduce

1. Install Drupal 11 with the standard profile.
2. Enable the language and content_translation modules.
3. Add a second language, for example Spanish (es). URL prefix negotiation is on by default, so /es/... sets the content language to es.
4. Make a media type translatable at /admin/config/regional/content-language.
5. Create an English media item of that type. Optionally save it again with "Create new revision" so there are several revisions. Do not add a Spanish translation.
6. Visit /media/{id}/revisions. It works.
7. Visit /es/media/{id}/revisions. You get a WSOD with InvalidArgumentException: Invalid translation language (es) specified.

Proposed resolution

Only call getTranslation() when the revision is a TranslatableInterface and hasTranslation($currentLangcode) is true. Otherwise, yield the revision unchanged. Add a kernel test covering a revision with no translation in the current language.