test: stabilize heap stats warmup

Retry JIT warmup before asserting executable heap stats so V8 tiering and GC timing do not leave the metric at zero.

Author: SamSaffron

test/mini_racer_test.rb

@@ -890,12 +890,16 @@ def test_estimated_size
     context.eval(<<~JS)
       let a='testing';
       let f=function(foo) { foo + 42 };
-
-      // call `f` a lot to have things JIT'd so that total_heap_size_executable becomes > 0
-      for (let i = 0; i < 1000000; i++) { f(10); }
     JS
 
-    stats = context.heap_stats
+    # whether JIT'd code is on the heap when we measure depends on V8 tiering
+    # and GC timing, so warm up until total_heap_size_executable becomes > 0
+    stats = nil
+    5.times do
+      context.eval("for (let i = 0; i < 1000000; i++) { f(10); }")
+      stats = context.heap_stats
+      break if stats[:total_heap_size_executable] > 0
+    end
     # eg: {:total_physical_size=>1280640, :total_heap_size_executable=>4194304, :total_heap_size=>3100672, :used_heap_size=>1205376, :heap_size_limit=>1501560832}
     assert_equal(
       %i[