minor #17080 Fix doctrine bridge tests on older PHP versions (jakzal)

This PR was merged into the 2.8 branch.

Discussion
----------

Fix doctrine bridge tests on older PHP versions

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | f176156
| License       | MIT
| Doc PR        | -

`Foo::class` constant was introduced in PHP 5.5.

Commits
-------

6c68946 Fix doctrine bridge tests on older PHP versions

src/Symfony/Bridge/Doctrine/Tests/Form/Type/EntityTypeTest.php

@@ -616,7 +616,7 @@ public function testSubmitSingleNonExpandedStringCastableIdentifier()
 
         $this->persist(array($entity1, $entity2));
 
-        $field = $this->factory->createNamed('name', EntityType::class, null, array(
+        $field = $this->factory->createNamed('name', 'Symfony\Bridge\Doctrine\Form\Type\EntityType', null, array(
             'multiple' => false,
             'expanded' => false,
             'em' => 'default',
@@ -638,7 +638,7 @@ public function testSubmitSingleStringCastableIdentifierExpanded()
 
         $this->persist(array($entity1, $entity2));
 
-        $field = $this->factory->createNamed('name', EntityType::class, null, array(
+        $field = $this->factory->createNamed('name', 'Symfony\Bridge\Doctrine\Form\Type\EntityType', null, array(
             'multiple' => false,
             'expanded' => true,
             'em' => 'default',
@@ -664,7 +664,7 @@ public function testSubmitMultipleNonExpandedStringCastableIdentifierForExisting
 
         $this->persist(array($entity1, $entity2, $entity3));
 
-        $field = $this->factory->createNamed('name', EntityType::class, null, array(
+        $field = $this->factory->createNamed('name', 'Symfony\Bridge\Doctrine\Form\Type\EntityType', null, array(
             'multiple' => true,
             'expanded' => false,
             'em' => 'default',
@@ -695,7 +695,7 @@ public function testSubmitMultipleNonExpandedStringCastableIdentifier()
 
         $this->persist(array($entity1, $entity2, $entity3));
 
-        $field = $this->factory->createNamed('name', EntityType::class, null, array(
+        $field = $this->factory->createNamed('name', 'Symfony\Bridge\Doctrine\Form\Type\EntityType', null, array(
             'multiple' => true,
             'expanded' => false,
             'em' => 'default',
@@ -720,7 +720,7 @@ public function testSubmitMultipleStringCastableIdentifierExpanded()
 
         $this->persist(array($entity1, $entity2, $entity3));
 
-        $field = $this->factory->createNamed('name', EntityType::class, null, array(
+        $field = $this->factory->createNamed('name', 'Symfony\Bridge\Doctrine\Form\Type\EntityType', null, array(
             'multiple' => true,
             'expanded' => true,
             'em' => 'default',