Fix documentation for input and output tutorial (GH-8231)

The ValueError message ends with a period.
(cherry picked from commit 9cffdbf)

Co-authored-by: Lysandros Nikolaou <[email protected]>

Author: miss-islington

Doc/tutorial/inputoutput.rst

@@ -338,7 +338,7 @@ automatically fail. ::
    >>> f.read()
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
-   ValueError: I/O operation on closed file
+   ValueError: I/O operation on closed file.
 
 
 .. _tut-filemethods: