pgsql: Force synchronous commit to be enabled for all test_decodingtes

Force synchronous commit to be enabled for all test_decoding tests.

Without that the tests fail when forced to be run against a cluster
with synchronous_commit = off (as the WAL might not yet be flushed to
disk by the point logical decoding gets called, and thus the expected
output breaks). Most tests already do that, add it to a few newer tests.

Author: Andres Freund

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/ef493055b67d30393a71c59d6fcbc2bd406528c2

Modified Files
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contrib/test_decoding/expected/truncate.out        | 2 ++
contrib/test_decoding/specs/oldest_xmin.spec       | 2 ++
contrib/test_decoding/specs/snapshot_transfer.spec | 2 ++
contrib/test_decoding/sql/truncate.sql             | 3 +++
4 files changed, 9 insertions(+)