Fix exiting from editing todo archive file (bug#32437)

Fix exiting from editing todo archive file (bug#32437)

* lisp/calendar/todo-mode.el (todo-edit-file): Make the warning
also suitable for Todo Archive mode, and add more space to it.
(todo-edit-quit): On quitting editing an archive file, return to
the Todo Archive mode buffer editing was invoked in.
(todo-check-format): Display a warning instead of a message when
the categories sexp isn't as expected.
(todo-mode-external-set): Remove.
(todo-edit-mode): Set buffer local values of
todo-current-todo-file and todo-categories from the todo or
archive file being edited.
(todo-categories-mode): Set buffer local values of
todo-current-todo-file and todo-categories as before but directly
instead of using superfluous todo-mode-external-set function.

* test/lisp/calendar/todo-mode-tests.el (todo-test-edit-quit): New test.