[3.13] gh-126259: Fix "unclosed database" warning in sqlite3 doctest (GH-126260) (#126265)

(cherry picked from commit 295262c8ec)

Co-authored-by: sobolevn <mail@sobolevn.me>

Doc/library/sqlite3.rst

@@ -2460,6 +2460,7 @@ 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: