Add testcase for sibling modules.

Closes PR 13155.

collects/tests/typed-racket/succeed/pr13155.rkt

@@ -0,0 +1,15 @@
+#lang racket/base
+
+(module defs typed/racket/base
+  (provide foo)
+  (: foo Integer)
+  (define foo 4)
+  )
+
+(module private-defs typed/racket/base
+  (require (submod ".." defs))
+  (provide foo)
+  )
+
+(require 'private-defs)
+foo