pgsql: Fix instability with WAL fsync test in stats.sql

Fix instability with WAL fsync test in stats.sql

A backend using wal_sync_method set to "open_sync" or "open_datasync"
would fail the test checking the WAL sync data in pg_stat_io. These
modes guarantee that a sync is done when WAL is written to disk, and the
data checked by the test is not incremented in this case,
issue_xlog_fsync() doing nothing.

Oversight in commit a051e71e28a1.

Author: Sami Imseih <samimseih(at)gmail(dot)com>
Discussion: https://postgr.es/m/CAA5RZ0uxwg3xAi4nvdBMJ-zJQEeyg+RotuU+ebM2F6CKmnvaYA@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/fdb69dd582427e4976897d544867e65a0e767002

Modified Files
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src/test/regress/expected/stats.out | 1 +
src/test/regress/sql/stats.sql | 1 +
2 files changed, 2 insertions(+)