Reduce number of iterations in TestFiberScheduler#test_autoload. (#…

…8391)

`ppc64le` appears to be struggling with this test due to timeout. Let's see
if reducing the number of iterations can help improve the test performance.

test/fiber/test_scheduler.rb

@@ -118,7 +118,7 @@ def test_current_scheduler
   end
 
   def test_autoload
-    100.times do
+    10.times do
       Object.autoload(:TestFiberSchedulerAutoload, File.expand_path("autoload.rb", __dir__))
 
       thread = Thread.new do