pgsql: Added literal tag for RETURNING

Added literal tag for RETURNING

This is an old mistake (92e38182d7c8); backpatch all the way back.

Author: Atsushi Torikoshi <torikoshia@oss.nttdata.com>
Reviewed-by: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
Discussion: https://postgr.es/m/c0aa00b60a16c0ea2a4c5123b013acb9@oss.nttdata.com

Branch
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REL_12_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/35cc9f15908f554d6fddc641536b63414eae234e

Modified Files
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doc/src/sgml/ref/copy.sgml | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)