Skip fpsig_fork_test on ptrace platform.
Skip fpsig_fork_test on ptrace platform.

There was a kernel bug introduced in 43be46e89698
("x86/fpu: Sanitize xstateregs_set()") which is causing
this test to break on ptrace platform. This commit was
bisected by Andrei Vagin.

Quoting Andrei: "The problem is that mxcsr isn't
changed if a new fpstate doesn't have one of SSE,
YMM, FP features."

PiperOrigin-RevId: 460543091

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