Lock TaskSet mutex for writing in ptraceClone().
Lock TaskSet mutex for writing in ptraceClone().

This is necessary since ptraceClone() mutates tracer.ptraceTracees.

PiperOrigin-RevId: 365152396

google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor