pgsql: Fix double table_close of sequence_rel in copy_sequences().

Fix double table_close of sequence_rel in copy_sequences().

sequence_rel was declared at batch scope, so when a row is skipped due to
concurrent drop or insufficient privileges, the end-of-row cleanup closes
the stale pointer from the previous row, tripping the relcache refcount
assertion.

Move sequence_rel inside the per-row loop.

Author: Ayush Tiwari <ayushtiwari(dot)slg01(at)gmail(dot)com>
Reviewed-by: vignesh C <vignesh21(at)gmail(dot)com>
Reviewed-by: Hayato Kuroda <kuroda(dot)hayato(at)fujitsu(dot)com>
Discussion: https://postgr.es/m/CAJTYsWWOuw-yfmzotV4jCJ6LLxEsb=STLcGtDYXOxRcU9Te3Pw@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/2bf6c9ff71c976d0a9fb6c31d6e1da02550b5278

Modified Files
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src/backend/replication/logical/sequencesync.c | 6 ++--
src/test/subscription/t/036_sequences.pl | 39 ++++++++++++++++++++++++++
2 files changed, 42 insertions(+), 3 deletions(-)