pythongh-120078: Fix struct_time attr typo tm_day -> tm_mday in Doc/library/time.rst (pythonGH-120081)

(cherry picked from commit b6b0dcb)

Co-authored-by: shurj0 <60540027+shurj0@users.noreply.github.com>

Author: shoenot

Doc/library/time.rst

@@ -617,7 +617,7 @@ Functions
         - range [1, 12]
 
       * - 2
-        - .. attribute:: tm_day
+        - .. attribute:: tm_mday
         - range [1, 31]
 
       * - 3