[4.1.x] Fixed #33958 -- Added imports to examples in "Expressions can reference transforms" section.

Backport of 411a6ec93a from main

docs/topics/db/queries.txt

@@ -701,15 +701,18 @@ Django supports using transforms in expressions.
 For example, to find all ``Entry`` objects published in the same year as they
 were last modified::
 
+    >>> from django.db.models import F
     >>> Entry.objects.filter(pub_date__year=F('mod_date__year'))
 
 To find the earliest year an entry was published, we can issue the query::
 
+    >>> from django.db.models import Min
     >>> Entry.objects.aggregate(first_published_year=Min('pub_date__year'))
 
 This example finds the value of the highest rated entry and the total number
 of comments on all entries for each year::
 
+    >>> from django.db.models import OuterRef, Subquery, Sum
     >>> Entry.objects.values('pub_date__year').annotate(
     ...     top_rating=Subquery(
     ...         Entry.objects.filter(