gh-110131: Restore the "for the option" scope in argparse's append docs

Before GH-131389 the bullet read "the default elements will be present in
the parsed value for the option".  That copyedit rewrote the sentence and
added an example, and the qualifier went with it, which left the bullet
claiming something that does not hold for positionals: append with
nargs='*' or '?' and default=['X'] gives ['X', ['X']] on empty input,
because the default is applied twice.

gh-110131 is filed against both 'append' and 'extend', so put the scope
back rather than leave the two bullets disagreeing about it.

Author: v0ropaev

Doc/library/argparse.rst

@@ -791,9 +791,9 @@ how the command-line arguments should be handled. The supplied actions are:
 
 * ``'append'`` - This appends each argument value to a list.
   It is useful for allowing an option to be specified multiple times.
-  If the default value is a non-empty list, the parsed value will start
-  with the default list's elements and any values from the command line
-  will be appended after those default values. Example usage::
+  If the default value is a non-empty list, the parsed value for the option
+  will start with the default list's elements and any values from the
+  command line will be appended after those default values. Example usage::
 
     >>> parser = argparse.ArgumentParser()
     >>> parser.add_argument('--foo', action='append', default=['0'])