pgsql: Update copyright for 2026

Update copyright for 2026

Backpatch-through: 14

Branch
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REL_17_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/625e4495bf58733f1dac24e363b12e6f95d7e92d

Modified Files
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COPYRIGHT | 2 +-
doc/src/sgml/legal.sgml | 6 +++---
2 files changed, 4 insertions(+), 4 deletions(-)