minor #23852 Made some SecurityBundle tests case-insensitive to prepare for future Symfony versions (javiereguiluz)

This PR was squashed before being merged into the 3.4 branch (closes #23852).

Discussion
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Made some SecurityBundle tests case-insensitive to prepare for future Symfony versions

| Q             | A
| ------------- | ---
| Branch?       | 3.4
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

This is what @nicolas-grekas [told me to do](https://github.com/symfony/symfony/pull/23797#issuecomment-320579781) to unlock #23797.

Commits
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9b7750a Made some SecurityBundle tests case-insensitive to prepare for future Symfony versions

src/Symfony/Bundle/SecurityBundle/Tests/DependencyInjection/CompleteConfigurationTest.php

@@ -81,6 +81,11 @@ abstract class CompleteConfigurationTest extends TestCase
             $configs[] = array_values($configDef->getArguments());
         }
 
+        // the IDs of the services are case sensitive or insensitive depending on
+        // the Symfony version. Transform them to lowercase to simplify tests.
+        $configs[0][2] = strtolower($configs[0][2]);
+        $configs[2][2] = strtolower($configs[2][2]);
+
         $this->assertEquals(array(
             array(
                 'simple',