pgsql: doc: Reword ALTER TABLE ATTACH restriction on NO INHERIT constra

doc: Reword ALTER TABLE ATTACH restriction on NO INHERIT constraints

The previous wording is easy to read incorrectly; this change makes it
simpler, less ambiguous, and less prominent.

Backpatch to all live branches.

Reviewed-by: Amit Langote 
Discussion: https://postgr.es/m/202411051201.zody6mld7vkw@alvherre.pgsql

Branch
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REL_15_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/d291e819be0c21691e5acfe000738b47deaaf0c9

Modified Files
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doc/src/sgml/ref/alter_table.sgml | 10 ++++------
1 file changed, 4 insertions(+), 6 deletions(-)