Reduce iteration count in thread torture test

Helps the test pass on 32 bit.

src/fish_tests.cpp

@@ -847,7 +847,7 @@ static void test_fd_monitor() {
 static void test_iothread() {
     say(L"Testing iothreads");
     std::unique_ptr<std::atomic<int>> int_ptr = make_unique<std::atomic<int>>(0);
-    int iterations = 50000;
+    int iterations = 64;
     int max_achieved_thread_count = 0;
     double start = timef();
     for (int i = 0; i < iterations; i++) {