pgsql: Turn off deprecated bison warnings under MSVC

Turn off deprecated bison warnings under MSVC

These are disabled by the configure code, so this is just fixing an
inconsistency in the MSVC code.

Backpatch to all live branches.

Branch
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REL_12_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/d0747714e6ef193c16d1acf31c15f387877d591f

Modified Files
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src/tools/msvc/pgbison.pl | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)