debian pipeline with make_signed_source tasks should not allow to upload packages when make_signed_source failed in some way

A build-pipeline workflow that is expected to sign some stuff will not wait for those sign jobs to succeed before proceeding to request a signature / upload the result. With manual signatures, the uploader can verify that everything went well, but this could be a problem with service keys and automatic uploads. For example in this pipeline, the sign jobs failed, yet the linux-6.1 build itself was waiting for a signature. I believe there should be a (possibly optional) barrier to wait for all sign jobs to succeed before uploading anything.

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