pgsql: doc PG 18 relnotes: Add incompatibility note about checksums now

doc PG 18 relnotes: Add incompatibility note about checksums now default

Reviewed-by: Tomas Vondra <tomas@vondra.me>
Discussion: /messages/by-id/CAKAnmmKwiMHik5AHmBEdf5vqzbOBbcwEPHo4-PioWeAbzwcTOQ@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/48814415d5aa0baa31622dd1ede9012e66232ca0

Modified Files
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doc/src/sgml/release-18.sgml | 21 +++++++++++++++++++++
1 file changed, 21 insertions(+)