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_17_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/1f0a58a0c21218e215df7847a08bdf75cf191abc

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