Fix untested contract generation code.

Closes PR 13449.

collects/tests/typed-racket/succeed/case-lambda-rest.rkt

@@ -0,0 +1,12 @@
+#lang racket/load
+
+(module a typed/racket
+  (provide foo)
+  (: foo
+     (case-> 
+       (Number String * -> Number)
+       (Number String String * -> Number)))
+  (define (foo x . args) x))
+
+(require 'a)
+(foo 3 "x")

collects/typed-racket/private/type-contract.rkt

@@ -190,7 +190,7 @@
                         (append (map t->c/neg (drop last-dom (length first-dom)))
                                 (append-map conv opt-kws)))]
                      [rng* (process-rngs (map t->c rngs))]
-                     [(rst-spec ...) (if rst #'(#:rest (listof #,(t->c/neg rest))) #'())])
+                     [(rst-spec ...) (if rst #`(#:rest (listof #,(t->c/neg rst))) #'())])
                   #'((dom* ...) (opt-dom* ...) rst-spec ... . ->* . rng*))])]
             [else
              (define ((f [case-> #f]) a)