msan: update shadow constant in strlen_of_shadow test

strlen_of_shadow hardcodes the mem-to-shadow
constant. That constant was changed in D137666;
this CL updates the test accordingly.
(Other tests will be updated separately.)

Differential Revision: https://reviews.llvm.org/D139027

GitOrigin-RevId: f5e2481b42fb4539232b5621adcfc03d2eeb4eb7
diff --git a/test/msan/strlen_of_shadow.cpp b/test/msan/strlen_of_shadow.cpp
index 5e7c89c..5257dc7 100644
--- a/test/msan/strlen_of_shadow.cpp
+++ b/test/msan/strlen_of_shadow.cpp
@@ -24,7 +24,7 @@
 #elif defined(__s390x__)
   return (char *)(((uintptr_t)p & ~0xC00000000000ULL) + 0x080000000000ULL);
 #elif defined(__aarch64__)
-  return (char *)((uintptr_t)p ^ 0x6000000000ULL);
+  return (char *)((uintptr_t)p ^ 0xB00000000000ULL);
 #endif
 }