Quarantine generate_distribution_shared_examples.rb

What does this MR do and why?

The spec failure has reoccurred in the recent master-broken incidents: gitlab-org/quality/engineering-productivity/master-broken-incidents#737 (closed) and gitlab-org/quality/engineering-productivity/master-broken-incidents#739 (closed).

To address the issue, this MR quarantines ./spec/workers/packages/debian/generate_distribution_worker_spec.rb until the root cause of the flakiness is identified and a solution is proposed.

Related to #389950 (closed)

How to set up and validate locally

bundle exec rspec spec/workers/packages/debian/generate_distribution_worker_spec.rb

MR acceptance checklist

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