6 files declare their use of SerializerInterface in Zircon Profile 8

GetSetMethodNormalizerTest.php in vendor/symfony/serializer/Tests/Normalizer/GetSetMethodNormalizerTest.php

ObjectNormalizerTest.php in vendor/symfony/serializer/Tests/Normalizer/ObjectNormalizerTest.php

PropertyNormalizerTest.php in vendor/symfony/serializer/Tests/Normalizer/PropertyNormalizerTest.php

Serializer.php in core/modules/rest/src/Plugin/views/style/Serializer.php

Contains \Drupal\rest\Plugin\views\style\Serializer.

SerializerAwareEncoder.php in vendor/symfony/serializer/Encoder/SerializerAwareEncoder.php

SerializerAwareNormalizer.php in vendor/symfony/serializer/Normalizer/SerializerAwareNormalizer.php