Declare return type of testcase setUp method

PHPUnit 7 changed the signature of the TestCase methods to include the
return type.

test/php/Nominatim/AddressDetailsTest.php

@@ -9,7 +9,7 @@ require_once(CONST_BasePath.'/lib/AddressDetails.php');
 class AddressDetailsTest extends \PHPUnit\Framework\TestCase
 {
 
-    protected function setUp()
+    protected function setUp(): void
     {
         // How the fixture got created
         //

test/php/Nominatim/DebugTest.php

@@ -7,7 +7,7 @@ require_once(CONST_BasePath.'/lib/DebugHtml.php');
 class DebugTest extends \PHPUnit\Framework\TestCase
 {
 
-    protected function setUp()
+    protected function setUp(): void
     {
         $this->oWithDebuginfo = $this->getMockBuilder(\GeococdeMock::class)
                                     ->setMethods(array('debugInfo'))

test/php/Nominatim/SearchContextTest.php

@@ -9,7 +9,7 @@ class SearchContextTest extends \PHPUnit\Framework\TestCase
     private $oCtx;
 
 
-    protected function setUp()
+    protected function setUp(): void
     {
         $this->oCtx = new SearchContext();
     }

test/php/Nominatim/TokenListTest.php

@@ -7,7 +7,7 @@ require_once(CONST_BasePath.'/lib/TokenList.php');
 
 class TokenTest extends \PHPUnit\Framework\TestCase
 {
-    protected function setUp()
+    protected function setUp(): void
     {
         $this->oNormalizer = $this->getMockBuilder(\MockNormalizer::class)
                                   ->setMethods(array('transliterate'))