Fix 1 occurrence of unless-expression-in-for-loop-to-unless-keyword

Use the `#:unless` keyword instead of `unless` to reduce loop body indentation.

Author: resyntax-ci[bot]

typed-racket-lib/typed-racket/static-contracts/optimize.rkt

@@ -342,10 +342,10 @@
     (unless (zero? (free-id-table-count to-look-at))
       (define new-table (make-free-id-table))
       (for* ([(id _) (in-free-id-table to-look-at)]
-             [(id _) (in-free-id-table (free-id-table-ref main-table id))])
-        (unless (free-id-table-ref seen id #f)
-          (free-id-table-set! seen id #t)
-          (free-id-table-set! new-table id #t)))
+             [(id _) (in-free-id-table (free-id-table-ref main-table id))]
+             #:unless (free-id-table-ref seen id #f))
+        (free-id-table-set! seen id #t)
+        (free-id-table-set! new-table id #t))
       (loop new-table)))
 
   ;; Determine if the recursive name is referenced in the static contract