Fix 1 occurrence of inverted-unless

This negated `unless` expression can be replaced by a `when` expression.

Author: resyntax-ci[bot]

typed-racket-lib/typed-racket/private/with-types.rkt

@@ -50,7 +50,7 @@
 (define (with-type-helper stx body fvids fvtys exids extys resty expr? ctx te-mode)
   (define old-context (unbox typed-context?))
   (define old-te-mode (unbox type-enforcement-mode))
-  (unless (not old-context)
+  (when old-context
     (tc-error/stx stx (format "with-type cannot be used in a typed module. ~a " old-context)))
   (set-box! typed-context? #t)
   (set-box! type-enforcement-mode te-mode)