Increase num_retries to reduce likelihood of test flake

Flakiness was observed in this build:
https://android-build.googleplex.com/builds/pending/P35853772/qemu_generic_arm32_gicv3_test_debug/latest/view/logs/build_error.log

But most other builds do not have this issue.

Bug: 234788755
Change-Id: I4cf7d05a56eb678164bf0006bfb190442d6d4e03
diff --git a/trusty/metrics/metrics_test.cpp b/trusty/metrics/metrics_test.cpp
index 407ddf2..9897950 100644
--- a/trusty/metrics/metrics_test.cpp
+++ b/trusty/metrics/metrics_test.cpp
@@ -31,7 +31,7 @@
 using android::base::unique_fd;
 
 static void TriggerCrash() {
-    size_t num_retries = 3;
+    size_t num_retries = 6;
     int fd = -1;
 
     for (size_t i = 0; i < num_retries; i++) {