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.

Doc/includes/sqlite3/parse_colnames.py

@@ -6,3 +6,5 @@ cur = con.cursor()
 cur.execute('select ? as "x [timestamp]"', (datetime.datetime.now(),))
 dt = cur.fetchone()[0]
 print(dt, type(dt))
+
+con.close()