Merge branch '5.0' into 5.1

* 5.0:
  Allow email message to have "To", "Cc", or "Bcc" header to be valid
  [FrameworkBundle] Removed detection of Serializer < 3.2
  Update pull request template for 5.1.
  [Security/Core] fix PHP8 deprecation

Tests/CacheWarmer/SerializerCacheWarmerTest.php

@@ -58,10 +58,6 @@ public function testWarmUpWithoutLoader()
      */
     public function testClassAutoloadException()
     {
-        if (!class_exists(CacheClassMetadataFactory::class) || !method_exists(XmlFileLoader::class, 'getMappedClasses') || !method_exists(YamlFileLoader::class, 'getMappedClasses')) {
-            $this->markTestSkipped('The Serializer default cache warmer has been introduced in the Serializer Component version 3.2.');
-        }
-
         $this->assertFalse(class_exists($mappedClass = 'AClassThatDoesNotExist_FWB_CacheWarmer_SerializerCacheWarmerTest', false));
 
         $warmer = new SerializerCacheWarmer([new YamlFileLoader(__DIR__.'/../Fixtures/Serialization/Resources/does_not_exist.yaml')], tempnam(sys_get_temp_dir(), __FUNCTION__));
@@ -86,10 +82,6 @@ public function testClassAutoloadExceptionWithUnrelatedException()
         $this->expectException(\DomainException::class);
         $this->expectExceptionMessage('This exception should not be caught by the warmer.');
 
-        if (!class_exists(CacheClassMetadataFactory::class) || !method_exists(XmlFileLoader::class, 'getMappedClasses') || !method_exists(YamlFileLoader::class, 'getMappedClasses')) {
-            $this->markTestSkipped('The Serializer default cache warmer has been introduced in the Serializer Component version 3.2.');
-        }
-
         $this->assertFalse(class_exists($mappedClass = 'AClassThatDoesNotExist_FWB_CacheWarmer_SerializerCacheWarmerTest', false));
 
         $warmer = new SerializerCacheWarmer([new YamlFileLoader(__DIR__.'/../Fixtures/Serialization/Resources/does_not_exist.yaml')], tempnam(sys_get_temp_dir(), __FUNCTION__));