By clicking on my submit, the php function is opening my file

I have the following file called test3.php:

<form action="cadastros.php" method="post">

<label for="latitude" hidden>Latitude:</label>
<input id="latMap" hidden name="latitude"/>

<label for="longitude" hidden>Longitude:</label>
<input id="lngMap" hidden name="longitude"/>

<input type="hidden" name="acao" value="inserir">

<input type="submit">

</form>

When I click submit, this function is called in my cadastros.php file:

if(isset($_POST['acao'])){
    if($_POST['acao'] == "inserir"){
    cadastraLatLong();
  }
}

function abrirBanco(){
    $conexao = new mysqli("localhost", "root", "", "cademeupet");
    return $conexao;
}

function cadastraLatLong(){
  $latitude = $_POST['latitude'];
  $longitude = $_POST['longitude'];

  $banco = abrirBanco();
  $sql = "INSERT INTO marcadores (id, descricao, lat, lng, tipo) VALUES (NULL, 'teste', '$latitude', '$longitude', 'testetipo')";
  $banco->query($sql);
  $banco->close();
  header('Location: teste3.php');
}

When I click the submit button, the cadastros.php file opens and displays the following: