bpo-41228: Fix /a/are/ in monthcalendar() descripton (GH-21372)

(cherry picked from commit 344dce3)

Co-authored-by: Nima Dini <[email protected]>

Author: miss-islington

Doc/library/calendar.rst

@@ -349,7 +349,7 @@ For simple text calendars this module provides the following functions.
 .. function:: monthcalendar(year, month)
 
    Returns a matrix representing a month's calendar.  Each row represents a week;
-   days outside of the month a represented by zeros. Each week begins with Monday
+   days outside of the month are represented by zeros. Each week begins with Monday
    unless set by :func:`setfirstweekday`.