[5.x] Fix toasts in actions not being shown

[jasonvarga]

When using the Toast facade in an action request, the toast would not be shown.

This is because the action requests were expecting blob types, not json, so they weren't being picked up.

I noticed this in #10264 when adding a toast in an EntryDeleting listener.

Event::listen(function (EntryDeleting $event) {
    Toast::error('Cannot save entry ['.$event->entry->title.'] because of a reason.');
    return false;
});

The action would complete, but the entry would be deleted, and you'd get no feedback. With this PR you will at least get the toast about why it wasn't deleted.

(In #10264 you will get feedback about the action not being successful too).