Fix stale runnable_hot_th hint causing assertion failure with MN threadsHEADmaster

The hot thread cannot steal back control when sched->running is an MN
thread, and goes to sleep with sched->runnable_hot_th still pointing to
itself, firing VM_ASSERT(sched->runnable_hot_th != th) at the next
wakeup. Drop the hint before sleeping since the thread is no longer
spinning. On a VM_CHECK_MODE build with RUBY_MN_THREADS=1:

    Thread.new { loop {} }
    100.times { File.read(IO::NULL) }

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

0 files changed, 0 insertions, 0 deletions