Fix misuse of expected in tc-keywords.

pkgs/typed-racket-pkgs/typed-racket-lib/typed-racket/typecheck/tc-app/tc-app-keywords.rkt

@@ -110,7 +110,7 @@
             arities doms rests drests rngs
             (stx-map tc-expr pos-args)
             #f #f #:expected expected
-            #:return (or expected (ret (Un)))
+            #:return (ret (Un))
             #:msg-thunk
             (lambda (dom)
               (string-append "No function domains matched in function application:\n"

pkgs/typed-racket-pkgs/typed-racket-test/tests/typed-racket/unit-tests/typecheck-tests.rkt

@@ -2688,6 +2688,17 @@
          #:ret (ret -String)
          #:expected (ret -String -no-filter -no-obj)]
 
+       [tc-err
+         (let ()
+           (: z (case->
+                  (-> Number #:b Symbol Number)
+                  (-> Symbol #:b Symbol Symbol)))
+           (define z (lambda (a #:b b) a))
+           (z "y" #:b "y"))
+         #:ret (ret -String)
+         #:expected (ret -String -no-filter -no-obj)]
+
+
         )
   (test-suite
    "tc-literal tests"