[GWP-ASan][Fuchsia] Use more modern zxtest testing macros

GitOrigin-RevId: 21fc42b2d594986a4ae28475b10c75bfe10d3bd2

tests/harness.h

diff --git a/tests/harness.h b/tests/harness.h
index 7129539..3e85935 100644
--- a/tests/harness.h
+++ b/tests/harness.h
@@ -12,6 +12,7 @@
 #include <stdarg.h>
 
 #if defined(__Fuchsia__)
+#define ZXTEST_USE_STREAMABLE_MACROS
 #include <zxtest/zxtest.h>
 namespace testing = zxtest;
 #else