[ledger] disable a flaky SynchronousTaskTest

The runs on fuchsia-x86_64-linux-debug fail with a crash in SynchronousTaskTest.RunSynchronouslyOnOtherThread:

https://ci.chromium.org/swarming/task/3962716b5afa6810?server=chromium-swarm.appspot.com

LE-335 #comment [ledger] disable a flaky SynchronousTaskTest

Change-Id: Ia835dec7ef4eb7d317ce3d373a2792fa97caab5c
diff --git a/bin/ledger/callback/synchronous_task_unittest.cc b/bin/ledger/callback/synchronous_task_unittest.cc
index 97810d2..63d71ed 100644
--- a/bin/ledger/callback/synchronous_task_unittest.cc
+++ b/bin/ledger/callback/synchronous_task_unittest.cc
@@ -10,7 +10,8 @@
 #include "lib/fsl/tasks/message_loop.h"
 #include "lib/fsl/threading/create_thread.h"
 
-TEST(SynchronousTaskTest, RunSynchronouslyOnOtherThread) {
+// Disabled as failing on the bots, see LE-335.
+TEST(SynchronousTaskTest, DISABLED_RunSynchronouslyOnOtherThread) {
   constexpr size_t nb_values = 1000;
   fxl::RefPtr<fxl::TaskRunner> task_runner;
   std::thread thread = fsl::CreateThread(&task_runner);