keys: Re-instate some RET bindings

* lisp/org-keys.el (org-mode-map): Re-instate S-RET and M-S-RET, which
are not translated from S-<return> and M-S-<return>, unlike
M-<return>/M-RET.

This is a followup to ee652a47df80b194c42ae27fff389a7b4debfaf7.

Reported-by: Kévin Le Gouguec <kevin.legouguec@gmail.com>

lisp/org-keys.el

@@ -454,7 +454,9 @@ COMMANDS is a list of alternating OLDDEF NEWDEF command names."
 
 ;;;; RET/<return> key with modifiers
 (org-defkey org-mode-map (kbd "S-<return>") #'org-table-copy-down)
+(org-defkey org-mode-map (kbd "S-RET") #'org-table-copy-down)
 (org-defkey org-mode-map (kbd "M-S-<return>") #'org-insert-todo-heading)
+(org-defkey org-mode-map (kbd "M-S-RET") #'org-insert-todo-heading)
 (org-defkey org-mode-map (kbd "M-RET") #'org-meta-return)
 
 ;;;; Cursor keys with modifiers