Add missing type declarations in soap tests

Author: nikic

ext/soap/tests/bug70388.phpt

@@ -5,7 +5,7 @@ soap
 --FILE--
 <?php
 class MySoapClient extends SoapClient {
-    public function __doRequest($request, $location, $action, $version, $one_way = 0) {
+    public function __doRequest($request, $location, $action, $version, $one_way = 0): string {
         echo $request, "\n";
         return '';
     }

ext/soap/tests/bugs/bug31755.phpt

@@ -5,7 +5,7 @@ soap
 --FILE--
 <?php
 class MySoapClient extends SoapClient {
-    public function __doRequest($request, $location, $action, $version, $one_way = 0) {
+    public function __doRequest($request, $location, $action, $version, $one_way = 0): string {
         echo $request, "\n";
         return '';
     }

ext/soap/tests/bugs/bug69085.phpt

@@ -8,7 +8,7 @@ soap.wsdl_cache_enabled=0
 <?php
 
 class MySoapClient extends SoapClient {
-    public function __doRequest($request, $location, $action, $version, $one_way = 0) {
+    public function __doRequest($request, $location, $action, $version, $one_way = 0): string {
         echo $request, "\n";
         return '';
     }

ext/soap/tests/bugs/bug77141.phpt

@@ -5,7 +5,7 @@ soap
 --FILE--
 <?php
 class MySoapClient extends SoapClient {
-    public function __doRequest($request, $location, $action, $version, $one_way = 0) {
+    public function __doRequest($request, $location, $action, $version, $one_way = 0): string {
         echo $request, "\n";
         return '';
     }