Fix Sphinx warnings

src/pretix/base/models/event.py

@@ -281,7 +281,7 @@ class Event(EventMixin, LoggedModel):
         self.cache.clear()
         return obj
 
-    def get_plugins(self) -> "list[str]":
+    def get_plugins(self):
         """
         Returns the names of the plugins activated for this event as a list.
         """

src/pretix/base/models/organizer.py

@@ -58,7 +58,7 @@ class Organizer(LoggedModel):
         self.get_cache().clear()
         return obj
 
-    def get_cache(self) -> "pretix.base.cache.ObjectRelatedCache":
+    def get_cache(self):
         """
         Returns an :py:class:`ObjectRelatedCache` object. This behaves equivalent to
         Django's built-in cache backends, but puts you into an isolated environment for