fix arity exception for a keyword procedure

Closes #3416

pkgs/racket-test-core/tests/racket/procs.rktl

@@ -773,6 +773,16 @@
   (test (list the-a the-b) the-b)
   (test 0 procedure-arity the-b))
 
+;; ----------------------------------------
+;; Make sure wrong number with keywords is an arity exception:
+
+(let ()
+  (define (hello a b #:key key) (display a))
+  (test #t
+        exn:fail:contract:arity?
+        (with-handlers ([values values])
+          (hello 1 #:key 'hi))))
+
 ;; ----------------------------------------
 
 (report-errs)

racket/collects/racket/private/kw.rkt

@@ -1578,7 +1578,7 @@
                                             (object-name p)
                                             p))])
                   (raise
-                   (exn:fail:contract
+                   ((if (or extra-kw missing-kw) exn:fail:contract exn:fail:contract:arity)
                     (if extra-kw
                         (if (keyword-procedure? p)
                             (format