pgsql: Last-minute updates for release notes.

Last-minute updates for release notes.

Security: CVE-2023-5868, CVE-2023-5869, CVE-2023-5870

Branch
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REL_12_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/8ff28255b6cd93b2fc3e12b12b05ed5430e48c4c

Modified Files
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doc/src/sgml/release-12.sgml | 115 ++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 114 insertions(+), 1 deletion(-)