[1.10.x] Fixed #27172 -- Closed database cursor explicitly in two doc examples

Backport of ccf7adb064a70eb1b1ec5857f1dd54988f5c983c from master.

docs/topics/db/managers.txt

@@ -67,7 +67,7 @@ returns a list of all ``OpinionPoll`` objects, each with an extra
     class PollManager(models.Manager):
         def with_counts(self):
             from django.db import connection
-            cursor = connection.cursor()
+            with connection.cursor() as cursor:
                 cursor.execute("""
                     SELECT p.id, p.question, p.poll_date, COUNT(*)
                     FROM polls_opinionpoll p, polls_response r

docs/topics/db/sql.txt

@@ -250,10 +250,8 @@ For example::
     from django.db import connection
 
     def my_custom_sql(self):
-        cursor = connection.cursor()
-
+        with connection.cursor() as cursor:
             cursor.execute("UPDATE bar SET foo = 1 WHERE baz = %s", [self.baz])
-
             cursor.execute("SELECT foo FROM bar WHERE baz = %s", [self.baz])
             row = cursor.fetchone()