minor symfony#58520 [Contracts] add missing properties (xabbuh)

This PR was merged into the 7.1 branch.

Discussion
----------

[Contracts] add missing properties

| Q             | A
| ------------- | ---
| Branch?       | 7.1
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Issues        |
| License       | MIT

Since symfony#54496 the property is no longer part of the `ServiceSubscriberTrait` triggering a PHP deprecation like:

> Creation of dynamic property Symfony\Contracts\Tests\Service\LegacyTestService::$container is deprecated

Commits
-------

fbfeefe add missing properties

Author: xabbuh

src/Symfony/Contracts/Tests/Service/LegacyTestService.php

@@ -33,6 +33,8 @@ class LegacyTestService extends LegacyParentTestService implements ServiceSubscr
 {
     use ServiceSubscriberTrait;
 
+    protected $container;
+
     #[SubscribedService]
     public function aService(): Service2
     {

src/Symfony/Contracts/Tests/Service/ServiceSubscriberTraitTest.php

@@ -56,6 +56,8 @@ public function testParentNotCalledIfHasMagicCall()
         };
         $service = new class() extends ParentWithMagicCall {
             use ServiceSubscriberTrait;
+
+            private $container;
         };
 
         $this->assertNull($service->setContainer($container));
@@ -69,6 +71,8 @@ public function testParentNotCalledIfNoParent()
         };
         $service = new class() {
             use ServiceSubscriberTrait;
+
+            private $container;
         };
 
         $this->assertNull($service->setContainer($container));