bpo-34580: Update sqlite3 examples to call close() explicitly (GH-9079)

The sqlit3.Connection object doesn't call its close() method when it's used
as a context manager.
diff --git a/Doc/includes/sqlite3/rowclass.py b/Doc/includes/sqlite3/rowclass.py
index 92b5ad6..fc60287 100644
--- a/Doc/includes/sqlite3/rowclass.py
+++ b/Doc/includes/sqlite3/rowclass.py
@@ -10,3 +10,5 @@
     assert row["name"] == row["nAmE"]
     assert row[1] == row["age"]
     assert row[1] == row["AgE"]
+
+con.close()