Disable type_checker_perf fast test

Fails on bot.

SR-6518

Author: aschwaighofer

validation-test/Sema/type_checker_perf/fast/rdar33806601.swift

@@ -1,6 +1,9 @@
 // RUN: %target-typecheck-verify-swift -solver-expression-time-threshold=1
 // REQUIRES: tools-release,no_asserts
 
+// FIXME: https://bugs.swift.org/browse/SR-6518
+// REQUIRES: SR6518
+
 class P {
   var x : Int = 0
   var y : Int = 1