pgsql: doc: clarify that max_wal_size is "during" checkpoints

doc: clarify that max_wal_size is "during" checkpoints

Previous wording was "between".

Reported-by: Pavel Luzanov

Discussion: /messages/by-id/26906a54-d7cb-2f8e-eed7-e31660024694@postgrespro.ru

Backpatch-through: 9.5

Branch
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REL_12_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/e3646325f4b6ca78c0a4234bf978cfda53721e4d

Modified Files
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doc/src/sgml/config.sgml | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)