[test] Fix test: add in explicit mkdir

validation-test/stdlib/StringNormalization.swift

@@ -9,6 +9,7 @@
 // See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
 //
 //===----------------------------------------------------------------------===//
+// RUN: mkdir -p %t
 // RUN: %target-build-swift %s -o %t/a.out
 // RUN: %target-run %t/a.out %S/Inputs/NormalizationTest.txt
 // REQUIRES: executable_test