fix(budget): name the category parking and file parking bookings in it

The key was 'parkings', which is not a word and does not match the 'parking'
the reservation type uses everywhere else. The shared trip page prints the
stored category verbatim, so a share link would have shown "parkings" in every
language.

The category also had no relationship to the booking type of the same name:
RESERVATION_TYPE_TO_COST_CATEGORY still sent a parking booking's auto-expense
to Transport, so the new bucket sat empty next to the costs that belong in it
while a manually typed "parking" resolved into it. Both paths agree now.

shared/src/i18n/de/budget.ts

@@ -121,7 +121,7 @@ const budget: TranslationStrings = {
   'costs.cat.health': 'Gesundheit',
   'costs.cat.tips': 'Trinkgeld',
   'costs.cat.fuel': 'Kraftstoff',
-  'costs.cat.parkings': 'Parken',
+  'costs.cat.parking': 'Parken',
   'costs.cat.other': 'Sonstiges',
   'costs.daysCount': '{count} Tage',
   'costs.travelers': '{count} Reisende',