Testing fallout for fixing SR-1903

Author: phausler

validation-test/stdlib/String.swift

@@ -1157,7 +1157,7 @@ StringTests.test("indexConversion")
   ) {
     result, flags, stop
   in
-    let r = result!.range(at: 1)
+    let r = result!.rangeAt(1)
     let start = String.UTF16Index(_offset: r.location)
     let end = String.UTF16Index(_offset: r.location + r.length)
     matches.append(String(s.utf16[start..<end])!)