lisp/org-num.el: Autoload safe variables

* lisp/org-num.el (org-num-face):
(org-num-max-level):
(org-num-skip-commented):
(org-num-skip-footnotes):
(org-num-skip-tags):
(org-num-skip-unnumbered): Autoload variables with :safe
specification.  Without autoloading, if org-num is not loaded,
unexpected warning may be displayed when opening an Org file.

Reported-by: Chang Xiaoduan <drcxd@sina.com>
Link: https://list.orgmode.org/orgmode/87jznf7gqo.fsf@PWRD-20230207OU./

lisp/org-num.el

@@ -83,6 +83,7 @@
 
 ;;; Customization
 
+;;;###autoload
 (defcustom org-num-face nil
   "Face to use for numbering.
 When nil, use the same face as the headline.  This value is
@@ -104,6 +105,7 @@ Any `face' text property on the returned string overrides
   :package-version '(Org . "9.3")
   :type 'function)
 
+;;;###autoload
 (defcustom org-num-max-level nil
   "Level below which headlines are not numbered.
 When set to nil, all headlines are numbered."
@@ -113,6 +115,7 @@ When set to nil, all headlines are numbered."
                  (integer :tag "Stop numbering at level"))
   :safe (lambda (val) (or (null val) (wholenump val))))
 
+;;;###autoload
 (defcustom org-num-skip-commented nil
   "Non-nil means commented sub-trees are not numbered."
   :group 'org-appearance
@@ -120,6 +123,7 @@ When set to nil, all headlines are numbered."
   :type 'boolean
   :safe #'booleanp)
 
+;;;###autoload
 (defcustom org-num-skip-footnotes nil
   "Non-nil means footnotes sections are not numbered."
   :group 'org-appearance
@@ -127,6 +131,7 @@ When set to nil, all headlines are numbered."
   :type 'boolean
   :safe #'booleanp)
 
+;;;###autoload
 (defcustom org-num-skip-tags nil
   "List of tags preventing the numbering of sub-trees.
 
@@ -141,6 +146,7 @@ control tag inheritance."
   :type '(repeat (string :tag "Tag"))
   :safe (lambda (val) (and (listp val) (cl-every #'stringp val))))
 
+;;;###autoload
 (defcustom org-num-skip-unnumbered nil
   "Non-nil means numbering obeys to UNNUMBERED property."
   :group 'org-appearance