gVisor BuildKite `pre-command`: Clean Docker `RUNTIME` to not contain slashes.
gVisor BuildKite `pre-command`: Clean Docker `RUNTIME` to not contain slashes.

Slashes in Docker runtime names break Docker.

PiperOrigin-RevId: 456642822

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