pgsql: Fix assorted doc typos

Fix assorted doc typos

Erik Rijkers and Justin Pryzby

Backpatch to v14

Discussion: https://www.postgresql.org/message-id/b79bfeff-d0e3-29a3-2576-0e325848dede%40xs4all.nl

Branch
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REL_15_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/b25566ab3c6536040df4df3ad99dd69c812215d9

Modified Files
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doc/src/sgml/brin.sgml               | 2 +-
doc/src/sgml/ref/drop_extension.sgml | 4 ++--
2 files changed, 3 insertions(+), 3 deletions(-)