Checkbox limitation in PHP table while loop not working

I have this scrip, and i want to check only two checkbox. But not working, and I don't know why.

(Sorry my english, this is not my first languages :( )

This is the php code, with the while loop table creation.

 <?php
include "connection.php";
$sql = "SELECT * FROM $tablename";
if($result = mysqli_query($mysqli, $sql)){
    if(mysqli_num_rows($result) > 0){
        echo "<table>";
            echo "<tr>";
                echo "<th>nev</th>";
                echo "<th>hely</th>";
                echo "<th>size</th>";
                echo "<th>valasztas</th>";
            echo "</tr>";          
        while($row = mysqli_fetch_array($result)){
            echo "<tr>";
                echo "<td>" . $row['nev'] . "</td>";
                echo "<td>" . $row['hely'] . "</td>";
                echo "<td>" . $row['size'] . "</td>";
                echo "<td><input type='checkbox' class='single-checkbox' name='checkbox[]' /></td>";
            echo "</tr>";
        }
        echo "</table>";
        // Free result set
        mysqli_free_result($result);
    } else{
        echo "No records matching your query were found.";
    }
} else{
    echo "ERROR: Could not able to execute $sql. " . mysqli_error($link);
}
  
mysqli_close($mysqli);
?>

And this is the code whit the jquery script.

<script type="text/javascript">
$(document).ready(function(){
  $('.single-checkbox').on('change', function(evt) {
     if ($('input[type="checkbox"]:checked').length >= 2)  {
      this.checked = false;
    };
  });
});
 </script>