[ trivial ] fix typo: indexes

Author: andf-mongodb

source/reference/system-collections.txt

@@ -74,7 +74,7 @@ each database:
 
       Starting in MongoDB 4.2, ``<database>.system.indexes`` has been
       removed (access to the collection has been deprecated since 3.0).
-      To list the inndexes, use the :dbcommand:`listIndexes` command
+      To list the indexes, use the :dbcommand:`listIndexes` command
       instead.
 
 .. data:: <database>.system.profile