pgsql: Fix shadow variable in postgres.c

Fix shadow variable in postgres.c

-Wshadow=compatible-local is added by default since 0fe954c, and this
warning was detected under -DWRITE_READ_PARSE_PLAN_TREES.

Reviewed-by: David Rowley
Discussion: https://postgr.es/m/Y0Ya5SH0QiaO9kKG@paquier.xyz

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/4574eb9d38c69f4c90b5468f740ff22519752066

Modified Files
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src/backend/tcop/postgres.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)