Randomize the random number generator's seed used in redis-benchmark (#8174)

The pid of the benchmark process is used to randomize the random number generator's
seed. This ensures that when multiple benchmark processes are started at the same time
to generate load on a server, they use different seeds. This will ensure randomness in
the keys generated by different benchmark processes.

src/redis-benchmark.c

@@ -1676,7 +1676,7 @@ int main(int argc, const char **argv) {
 
     client c;
 
-    srandom(time(NULL));
+    srandom(time(NULL) ^ getpid());
     signal(SIGHUP, SIG_IGN);
     signal(SIGPIPE, SIG_IGN);