Use an explicit autoload form

Mostly to quickly fix the CI, but it could benefit some who install from git too.

Author: dgutov

diff-hl-margin.el

@@ -147,7 +147,6 @@ You probably shouldn't use this function directly."
                         ,(propertize char 'face
                                      (intern (format "diff-hl-margin-%s" type)))))))))
 
-;;;###autoload
 (defun diff-hl-highlight-on-margin (ovl type _shape)
   (let ((spec (cdr (assoc (cons type diff-hl-side)
                           (diff-hl-margin-spec-cache)))))

diff-hl.el

@@ -506,6 +506,8 @@ It can be a relative expression as well, such as \"HEAD^\" with Git, or
     (funcall diff-hl-highlight-function o type shape)
     o))
 
+(autoload 'diff-hl-highlight-on-margin "diff-hl-margin")
+
 (defun diff-hl-highlight-on-fringe (ovl type shape)
   (if (and diff-hl-fallback-to-margin
            (not (display-graphic-p)))