Ignore the result of pthread_kill in ubf_wakeup_thread
After an upgrade to Ruby 3.3.0, I experienced reproducible production crashes
of the form:
[BUG] pthread_kill: No such process (ESRCH)
This is the only pthread_kill call in Ruby. The result of pthread_kill was
previously ignored in Ruby 3.2 and below. Checking the result was added in
be1bbd5b7d40ad863ab35097765d3754726bbd54 (MaNy).
I have not yet been able to create a minimal self-contained example,
but it should be safe to remove the checks.
merge revision(s) ef3803ed4028810f9088019f0db1a366370ab53a: [Backport #20502]