build(sf): prepare for 7.0

[Guikingone]

It seems to fix the issue thank you.

While you're at it, you may also want to already add the context parameters to methods supportsNormalization && supportsDenormalization to handle the following deprecation notice for all your instances of NormalizerInterface & DenormalizerInterface

The "SchedulerBundle\Serializer\TaskNormalizer::supportsNormalization()" method will require a new "array $context" argument in the next major version of its interface "Symfony\Component\Serializer\Normalizer\NormalizerInterface", not defining it is deprecated.

Originally posted by @nfragnet in #259 (comment)

[jmsche]

This deprecation should be handled by #266