For performance reasons, mutation_partition_v2::maybe_drop(), and by extension
also mutation_partition_v2::apply_monotonically(mutation_partition_v2&&)
can evict empty row entries, and hence change the continuity of the merged
entry.
For checking that apply_to_incomplete respects continuity,
test_apply_to_incomplete_respects_continuity obtains the continuity of
the partition entry before and after apply_to_incomplete by calling
e.squashed().get_continuity(). But squashed() uses apply_monotonically(),
so in some circumstances the result of squashed() can have smaller
continuity than the argument of squashed(), which messes with the thing
that the test is trying to check, and causes spurious failures.
This patch changes the method of calculating the continuity set,
so that it matches the entry exactly, fixing the test failures.
Fixesscylladb/scylladb#13757Closesscylladb/scylladb#21459
(cherry picked from commit 35921eb67e)
Closesscylladb/scylladb#21497