Change socket creation failure test

Since Gitlab's runners possess the root privileges, it is more tricky
to get a "Permission denied".

Instead, we try to create two servers listening to the same port which
leads to an "Address already in use"

tests/test_Socket.cpp

@@ -75,7 +75,10 @@ TEST_CASE("Socket", "[utils]")
   {
     SECTION("connection")
     {
-      REQUIRE_THROWS_WITH(createServerSocket(1), "error: Permission denied");
+      {
+        auto server = createServerSocket(0);
+        REQUIRE_THROWS_WITH(createServerSocket(server.portNumber()), "error: Address already in use");
+      }
       REQUIRE_THROWS_WITH(connectServerSocket("localhost", 1), "error: Connection refused");
 
       // The error message is not checked since it can depend on the