Run ptrace stubs in their own session and process group.
Run ptrace stubs in their own session and process group.

Pseudoterminal job control signals are meant to be received and handled by the
sandbox process, but if the ptrace stubs are running in the same process group,
they will receive the signals as well and inject then into the sentry kernel.

This can result in duplicate signals being delivered (often to the wrong
process), or a sentry panic if the ptrace stub is inactive.

This CL makes the ptrace stub run in a new session.

PiperOrigin-RevId: 218536851
Change-Id: Ie593c5687439bbfbf690ada3b2197ea71ed60a0e

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