Unbreak Pbkdf2PasswordTest

Due to sebastianbergmann/phpunit#3459 it was
looking for a wrong function name and was skipping the test even when PHP
support was present.

Change-Id: I2508f192a76275286e95bd6a06e4628d98b11737

tests/phpunit/includes/password/Pbkdf2PasswordTest.php

@@ -5,9 +5,17 @@
  * @covers Pbkdf2Password
  * @covers Password
  * @covers ParameterizedPassword
- * @requires function hash_pbkdf2
  */
 class Pbkdf2PasswordTest extends PasswordTestCase {
+	public function setUp() {
+		parent::setUp();
+		// Can't be done with annotations due to
+		// https://github.com/sebastianbergmann/phpunit/issues/3459
+		if ( !function_exists( 'hash_pbkdf2' ) ) {
+			$this->markTestSkipped( 'function hash_pbkdf2 is required' );
+		}
+	}
+
 	protected function getTypeConfigs() {
 		return [ 'pbkdf2' => [
 			'class' => Pbkdf2Password::class,