Fix the signature for gopark.
Fix the signature for gopark.

gopark's signature was changed from having a string reason to a
uint8.

See: https://github.com/golang/go/commit/4d7cf3fedbc382215df5ff6167ee9782a9cc9375

This broke execution tracing of the sentry.

Switching to the right signature makes tracing work again.

Updates #220

PiperOrigin-RevId: 249565311
Change-Id: If77fd276cecb37d4003c8222f6de510b8031a074

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