pgsql: doc: Mention validation attempt during ALTER INDEX .. ATTACH PAR

doc: Mention validation attempt during ALTER INDEX .. ATTACH PARTITION

Since 9d3e094f12, the command tries to validate the parent index of the
named index, if invalid. The documentation did not mention this
behavior, which could be confusing.

Author: Mohamed ALi <moali.pg@gmail.com>
Discussion: /messages/by-id/CAGnOmWpHu25_LpT=zv7KtetQhqV1QEZzFYLd_TDyOLu1Od9fpw@mail.gmail.com
Backpatch-through: 14

Branch
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REL_16_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/8f2429ff24feeec6ddcf0f20f125aa35ebced0c9

Modified Files
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doc/src/sgml/ref/alter_index.sgml | 5 +++++
1 file changed, 5 insertions(+)