Disable Span bounds check elimination tests for asserts builds

The asserts introduce null pointer checks that make the test too fragile.

Author: stephentyrone

test/stdlib/Span/BoundsCheckOptimization.swift

@@ -11,6 +11,7 @@
 //===----------------------------------------------------------------------===//
 
 // RUN: %target-swift-frontend -primary-file %s -O -emit-assembly | %FileCheck %s --check-prefix CHECK --check-prefix CHECK-%target-cpu
+// REQUIRES: swift_stdlib_no_asserts
 
 import Swift