Description:
------------
When I pass an array of headers to __setSoapHeaders, subsequent calls do not overwrite the previous headers. It works correctly when I pass a single object to that method.

Test script:
---------------
<?php
$client = new \SoapClient(null, 
            [
                'trace' => 1,
                'exceptions' => true,
                'uri' => '',
                'location' => '',
            ]);
			
$client->__setSoapHeaders([new \SoapHeader('ns', 'Header', ['something' => 1])]);
$client->__setSoapHeaders([new \SoapHeader('ns', 'Header', ['something' => 2])]);

try {
	$client->__soapCall('SomeMethod', ['a' => 'b']);
} catch(\Exception $e) {
}

var_dump($client->__getLastRequest());
var_dump($client->__getLastRequestHeaders());

Expected result:
----------------
Can't post the whole XML because of spam detection, so just a fragment:

><SOAP-ENV:Header><ns2:Header><item><key>something</key><value>1</value></item></ns2:Header></SOAP-ENV:Header>

Actual result:
--------------
><SOAP-ENV:Header><ns2:Header><item><key>something</key><value>2</value></item></ns2:Header></SOAP-ENV:Header>