minor #17566 Change couple of occurences of a public setUp() method to protected (jakzal)

This PR was merged into the 2.7 branch.

Discussion
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Change couple of occurences of a public setUp() method to protected

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

`setUp()` is a protected method. There's no occurrences on the 2.3 branch.

Commits
-------

5fe7359 Change couple of occurences of a public setUp() method to protected

src/Symfony/Bridge/Twig/Tests/AppVariableTest.php

@@ -13,7 +13,7 @@ class AppVariableTest extends \PHPUnit_Framework_TestCase
      */
     protected $appVariable;
 
-    public function setUp()
+    protected function setUp()
     {
         $this->appVariable = new AppVariable();
     }

src/Symfony/Component/DependencyInjection/Tests/Compiler/ExtensionCompilerPassTest.php

@@ -21,7 +21,7 @@ class ExtensionCompilerPassTest extends \PHPUnit_Framework_TestCase
     private $container;
     private $pass;
 
-    public function setUp()
+    protected function setUp()
     {
         $this->container = $this->getMock('Symfony\Component\DependencyInjection\ContainerBuilder');
         $this->pass = new ExtensionCompilerPass();