chore: Translate pressbooks-multi-institution.pot in ja

92% of minimum 25% translated source file: 'pressbooks-multi-institution.pot'
on 'ja'.

Sync of partially translated files: 
untranslated content is included with an empty translation 
or source language content depending on file format

languages/pressbooks-multi-institution-ja.po

@@ -349,7 +349,7 @@ msgstr ""
 
 #: resources/views/institutions/form.blade.php:207
 msgid "Premium Member Buy-in"
-msgstr ""
+msgstr "プレミアムメンバーバイイン"
 
 #: resources/views/institutions/form.blade.php:227
 msgid "Book Limit"