Issue #18452: fix several "occurrence" typos (reported by Févry Thibault).

Doc/howto/argparse.rst

@@ -468,7 +468,7 @@ verbosity argument (check the output of ``python --help``)::
        print answer
 
 We have introduced another action, "count",
-to count the number of occurences of a specific optional arguments:
+to count the number of occurrences of a specific optional arguments:
 
 .. code-block:: sh
 

Doc/library/stdtypes.rst

@@ -743,10 +743,10 @@ are sequences of the same type; *n*, *i* and *j* are integers:
 +------------------+--------------------------------+----------+
 | ``max(s)``       | largest item of *s*            |          |
 +------------------+--------------------------------+----------+
-| ``s.index(i)``   | index of the first occurence   |          |
+| ``s.index(i)``   | index of the first occurrence  |          |
 |                  | of *i* in *s*                  |          |
 +------------------+--------------------------------+----------+
-| ``s.count(i)``   | total number of occurences of  |          |
+| ``s.count(i)``   | total number of occurrences of |          |
 |                  | *i* in *s*                     |          |
 +------------------+--------------------------------+----------+