[test] Collection tests with reference types should also require optimized stdlib

Author: lorentey

validation-test/stdlib/Collection/Inputs/Template.swift.gyb

@@ -127,6 +127,10 @@ runAllTests()
 // RUN: %target-run-simple-swift
 // REQUIRES: executable_test
 
+// FIXME: the test is too slow when the standard library is not optimized.
+// rdar://problem/46878013
+// REQUIRES: optimized_stdlib
+
 import StdlibUnittest
 import StdlibCollectionUnittest