pgsql: Fix signedness error in 9f225e992 for gcc

Fix signedness error in 9f225e992 for gcc

The first argument of vshrq_n_s8 needs to be a signed vector type,
but it was passed unsigned. Clang is more lax with conversion, but
gcc needs a cast.

Fix by me, tested by Masahiko Sawada

Per buildfarm members splitfin, batta, widowbird, snakefly, parula,
massasauga

Discussion: https://postgr.es/m/20240306074106.mg6w4koohdlworbs%40alap3.anarazel.de

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/de7c6fe8347ab726c80ebbfcdb57f4b714d5243d

Modified Files
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src/include/port/simd.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)