Disable SIMDConcreteFP.swift.gyb (76545659)

This test is taking 60+ mins to execute in https://ci.swift.org/job/oss-swift_tools-RA_stdlib-RDA_test-simulator/

Author: shahmishal

test/stdlib/SIMDConcreteFP.swift.gyb

@@ -15,6 +15,7 @@
 // RUN: %target-codesign %t/a.out
 // RUN: %line-directive %t/SIMDConcreteFP.swift -- %target-run %t/a.out
 // REQUIRES: executable_test
+// REQUIRES: rdar76545659
 
 import StdlibUnittest