src/assets/i18n: update English strings

Re-word two messages for better English and consistency with other
similar strings.

Author: alanorth

src/assets/i18n/en.json5

@@ -1298,9 +1298,9 @@
 
   "community.all-lists.head": "Subcommunities and Collections",
 
-  "community.sub-collection-list.head": "Collections of this Community",
+  "community.sub-collection-list.head": "Collections in this Community",
 
-  "community.sub-community-list.head": "Communities of this Community",
+  "community.sub-community-list.head": "Communities in this Community",
 
   "cookies.consent.accept-all": "Accept all",