With previous design of the schema change test, a regeneration
was necessary each time a new distributed system table was added.
It was not the original purpose of the test to keep track of new
distributed tables which simply propagate on their own,
so the test case is now modified: internal distributed tables
are not part of the schema digest anymore, which means that
changes inside them will not cause mismatches.
This change involves a one-shot regeneration of all digests,
which due to historical reasons included internal distributed
tables in the digest, but no further regenerations should ever
be necessary when a new internal distributed table is added.
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