lang/org: set org-link-abbrev-alist non-destructively

So prior values aren't overwritten (and shadow these defaults), and also
because, due to the hook order, the attach: link was overwritten by this
setq.

modules/lang/org/config.el

@@ -356,7 +356,7 @@ file isn't in `org-directory'."
              'error)))
 
   ;; Add custom link types
-  (setq org-link-abbrev-alist
+  (nconcq! org-link-abbrev-alist
            '(("github"      . "https://github.com/%s")
              ("youtube"     . "https://youtube.com/watch?v=%s")
              ("google"      . "https://google.com/search?q=")