[lldb/test] Add yield to spin loop in thread_filter test (#191025)
This should fix:
https://lab.llvm.org/buildbot/#/builders/211/builds/7439
The timeout might be caused by three threads busy-spinning at 100% CPU,
starving the CI machine.
Add std::this_thread::yield() to the spin loop to reduce CPU pressure
while keeping threads alive at a debugger-friendly location.
Signed-off-by: Med Ismail Bennani <ismail@bennani.ma>