Revert "Remove unnecessary _fixLifetime"

This reverts commit ce17877d50.

stdlib/public/core/StringCreate.swift

@@ -124,6 +124,7 @@ extension String {
       // we use it directly. This could be a little faster, but this error path
       // shouldn't be perf-sensitive anyway.
       let temporaryCodeUnits = Array(result.codeUnits)
+      defer { _fixLifetime(temporaryCodeUnits) }
       return temporaryCodeUnits.withContiguousStorageIfAvailable {
         //This could be optimized to use excess tail capacity
         return repairUTF8($0, firstKnownBrokenRange: initialRange)