pythongh-126259: Fix "unclosed database" warning in sqlite3 doctest (p…

…ython#126260)

Doc/library/sqlite3.rst

@@ -2442,6 +2442,7 @@ Some useful URI tricks include:
    >>> con.execute("CREATE TABLE readonly(data)")
    Traceback (most recent call last):
    OperationalError: attempt to write a readonly database
+   >>> con.close()
 
 * Do not implicitly create a new database file if it does not already exist;
   will raise :exc:`~sqlite3.OperationalError` if unable to create a new file: