bug#66715: 30.0.50; Minor issues with Gnus defcustoms

[Mauro Aranda]

I went through the Gnus directory, and found the following issues with
its defcustoms:

- gnus-button-prefer-mid-or-mail: Says the value might be a function,
  but doesn't list that as a choice.

- gnus-bookmark-bookmark-inline-details: The docstring says (subject) is
  the default value, but it actually is (author).

- gnus-simplify-subject-fuzzy-regexp: Says the value might be a single
  regexp, but doesn't allow it.

- message-indent-citation-function: Says value might be a list of
  functions, but doesn't allow it.

- message-mail-alias-type: Says value might be a list, but doesn't allow
  it.

- message-dont-reply-to-names: Says value might be a function, but
  doesn't allow it.

- spam-report-url-ping-function: The default value for the function
  widget is nil, which is wrong.