raco setup: don't try to "sync" a doc that isn't pre-rendered

On my machine, the sync path was sometimes triggered for "htdp-ptr".
(I'm not sure why; progress toward determinsitic bytecode might
be relevant.) Adjust the trigger for sync mode to check that the
needed "provides.sxref" file exists.

pkgs/racket-index/setup/scribble.rkt

@@ -1062,7 +1062,10 @@
                                (and can-run?
                                     (not (equal? (car stamp-data)
                                                  src-sha1))
-                                    'newer)))]
+                                    'newer)
+                               (and (or (not provides-time)
+                                        (provides-time . < . info-out-time))
+                                    (not (file-exists? (build-path (doc-dest-dir doc) "provides.sxref"))))))]
          [up-to-date? (not out-of-date)]
          [can-run? (and src-zo
                         (or (not latex-dest)