lib/unixfd: Fix data race in unit test.
lib/unixfd: Fix data race in unit test.

Change-Id: Ic1d6640fe7da4d6b46f12a5fb26c17fdf67a7ae5

vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref