Merge branch '2.3-develop-phpunit9' of https://github.com/magento-commerce/magento2ce into MC-39898

Author: jcuerdo

dev/tests/static/testsuite/Magento/Test/Integrity/App/Language/TranslationFiles.php

@@ -15,7 +15,7 @@ class TranslationFiles extends \PHPUnit\Framework\TestCase
      */
     protected $csvParser;
 
-    protected function setUp() : void
+    protected function setUp(): void
     {
         $this->csvParser = new \Magento\Framework\File\Csv(new File());
     }

dev/tests/static/testsuite/Magento/Test/Legacy/LicenseTest.php

@@ -23,7 +23,7 @@ function ($filename) {
 
                 foreach ($matches[0] as $commentText) {
                     foreach (['Irubin Consulting Inc', 'DBA Varien', 'Magento Inc'] as $legacyText) {
-                        $this->assertNotContains(
+                        $this->assertStringNotContainsString(
                             $legacyText,
                             $commentText,
                             "The license of file {$filename} contains legacy text."

dev/tests/static/testsuite/Magento/Test/Legacy/TableTest.php

@@ -200,12 +200,12 @@ protected static function _matchesToInformation($content, $matches)
      * Composes information message based on list of legacy tables, found in a file
      *
      * @param  array $legacyTables
-     * @return null|string
+     * @return string
      */
-    protected function _composeFoundsMessage($legacyTables)
+    protected function _composeFoundsMessage($legacyTables): string
     {
         if (!$legacyTables) {
-            return null;
+            return '';
         }
 
         $descriptions = [];