lock: fix data race in (*SemaphoredMutexSuite).TestParallelism()
lock: fix data race in (*SemaphoredMutexSuite).TestParallelism()

In this case it's fine to use the global source (which is
concurrency-safe) as it is seeded with time.Now().UnixNano()

Closes #13569

Fixes: fac5ddea5007 ("rand: add and use concurrency-safe PRNG source")
Signed-off-by: Tobias Klauser <9249c549618448e4c699e8032ba6c7f0d7fd4b7f@distanz.ch>

tklauser/cilium,tklauser/cilium,tgraf/cilium,michi-covalent/cilium,tgraf/cilium,michi-covalent/cilium,tklauser/cilium,tgraf/cilium,cilium/cilium,michi-covalent/cilium,tklauser/cilium,michi-covalent/cilium,cilium/cilium,tklauser/cilium,cilium/cilium,cilium/cilium,michi-covalent/cilium,tgraf/cilium,tgraf/cilium,tgraf/cilium,cilium/cilium