ci: mark tcp_test.v and unix_socket_test.v as flaky (they still fail sporadically on the CI, although very rarely now)

vlib/net/tcp_test.v

@@ -1,3 +1,4 @@
+// vtest flaky: true
 // vtest retry: 5
 import net
 

vlib/net/unix/unix_socket_test.v

@@ -1,3 +1,5 @@
+// vtest flaky: true
+// vtest retry: 3
 import os
 import log
 import time