test/fiber/test_queue.rb: Make the stuck test fail. (#8791)

test/fiber/test_queue.rb: Make the stuck tests fail.

We observed the 2 tests in the `test/fiber/test_queue.rb` getting stuck
in some GCC compilers in Ubuntu ppc64le focal/jammy, even when the timeout
`queue.pop(timeout: 0.0001)` is set in the code.

This commit is to make the tests fail rather than getting stuck.

test/fiber/test_queue.rb

@@ -5,9 +5,10 @@ require_relative 'scheduler'
 class TestFiberQueue < Test::Unit::TestCase
   def test_pop_with_timeout
     queue = Thread::Queue.new
+    kill = false
     result = :unspecified
 
-    Thread.new do
+    thread = Thread.new do
       scheduler = Scheduler.new
       Fiber.set_scheduler(scheduler)
 
@@ -16,17 +17,23 @@ class TestFiberQueue < Test::Unit::TestCase
       end
 
       scheduler.run
-    end.join
+    end
+    until thread.join(2)
+      kill = true
+      thread.kill
+    end
 
+    assert_false(kill, 'Getting stuck due to a possible compiler bug.')
     assert_nil result
   end
 
   def test_pop_with_timeout_and_value
     queue = Thread::Queue.new
     queue.push(:something)
+    kill = false
     result = :unspecified
 
-    Thread.new do
+    thread = Thread.new do
       scheduler = Scheduler.new
       Fiber.set_scheduler(scheduler)
 
@@ -35,8 +42,13 @@ class TestFiberQueue < Test::Unit::TestCase
       end
 
       scheduler.run
-    end.join
+    end
+    until thread.join(2)
+      kill = true
+      thread.kill
+    end
 
+    assert_false(kill, 'Getting stuck due to a possible compiler bug.')
     assert_equal :something, result
   end
 end