Remove extra blank line in client_test.go

This change removes an unnecessary blank line at the end of the TestClient_sendSingleMsg function in the client_test.go file. Keeping the code clean and properly formatted improves readability and maintainability.

client_test.go

@@ -2816,7 +2816,6 @@ func TestClient_DialToSMTPClientWithContext(t *testing.T) {
 			t.Fatal("expected connection to fake to fail")
 		}
 	})
-
 }
 
 func TestClient_sendSingleMsg(t *testing.T) {