pgsql: Fix nbtree skip array transformation comments.

Fix nbtree skip array transformation comments.

Fix comments that incorrectly described transformations performed by the
"Avoid extra index searches through preprocessing" mechanism introduced
by commit b3f1a13f.

Author: Yugo Nagata <nagata@sraoss.co.jp>
Reviewed-By: Chao Li <li.evan.chao@gmail.com>
Reviewed-By: Peter Geoghegan <pg@bowt.ie>
Discussion: https://postgr.es/m/20251230190145.c3c88c5eb0f88b136adda92f@sraoss.co.jp
Backpatch-through: 18

Branch
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REL_18_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/6c99c715ddb338e169c2ffd2a4cf754fa510cccb

Modified Files
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src/backend/access/nbtree/nbtpreprocesskeys.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)