Merge data from qualifying rows of a 2d array into a flat associative array

I have a $_SESSION array which I filter/sanitize by keys inside of a loop. This produces a 2d array of qualifying data, but I want to reduce it to a flat associative array.

Theoretical input:

$_SESSION = [
    // ...some unwanted row
    'saved_query_something' => ['product_category' => 'for-women'],
    'saved_query_something_else' => ['brand' => '7-diamonds'],
    // ...some unwanted row
    'saved_query_blah' => ['size' => 12],
    'saved_query_blar' => ['color' => 882536],
];

This is my current code that doesn't correctly reduce the data structure while sanitizing.

foreach ($_SESSION as $k => $v) {
    if (strstr($k, 'saved_query_') == true) {
        $saved = array_merge($v);
    }
}

The desired result:

[
  'product_category' => 'for-women',
  'brand' => '7-diamonds',
  'size' => 12,
  'color' => 882536,
]

You can try using array_merge

$array0 = Array ( "product_category" => "for-women" );
$array1 = Array ( "brand" => "7-diamonds" ) ;
$array2 = Array ( "size" => "12" ) ;
$array3 = Array ( "color" => "882536" );

$array = array_merge($array0,$array1,$array2,$array3);

print_r($array);

Output

Array ( [product_category] => for-women [brand] => 7-diamonds [size] => 12 [color] => 882536 )

See Demo

* ----- Update ----- *

If you are looking through a session

$_SESSION = Array();
$_SESSION[0] = Array("product_category" => "for-women");
$_SESSION[1] = Array("brand" => "7-diamonds");
$_SESSION[2] = Array("size" => "12");
$_SESSION[3] = Array("color" => "882536");

$final = array();
foreach ( $_SESSION as $key => $value ) {
    $final = array_merge($final, $value);
}

print_r($final);