$('option').mousedown(function(e) {
    e.preventDefault();
    var originalScrollTop = $(this).parent().scrollTop();
    console.log(originalScrollTop);
    $(this).prop('selected', $(this).prop('selected') ? false : true);
    var self = this;
    $(this).parent().focus();
    setTimeout(function() {
        $(self).parent().scrollTop(originalScrollTop);
    }, 0);
    
    return false;
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/1.7/jquery.min.js"></script>
<div class="form-group">
      <label class="col-form-label">Select some options</label>
        <select class="form-control" id="aluno" multiple>
          <option selected="true" disabled>Click to select</option>
          <option>Option 1</option>
          <option>Option 2</option>
          <option>Option 3</option>
          <option>Option 4</option>
          <option>Option 5</option>
        </select>
    </div>