pgsql: doc: Correct the documented type of pg_get_multixact_stats().num

doc: Correct the documented type of pg_get_multixact_stats().num_mxids

The documentation listed num_mxids as integer, but its SQL type has
been bigint since the function was introduced. Correct the
documentation to match the actual return type.

Backpatch to v19, where the function was introduced.

Author: Naeem Akhter <naeem(dot)akhter(at)percona(dot)com>
Author: Noriyoshi Shinoda <noriyoshi(dot)shinoda(at)hpe(dot)com>
Reviewed-by: Naga Appani <nagnrik(at)gmail(dot)com>
Reviewed-by: Michael Paquier <michael(at)paquier(dot)xyz>
Reviewed-by: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
Discussion: https://postgr.es/m/CAKB0-TEcYJoUn8Q_nug8KEvC9Ea0FV_JOe8XwcW-9QrqUjaBxQ@mail.gmail.com
Discussion: https://postgr.es/m/LV8PR84MB3787CF6E56DCC99AE23E712EEE242@LV8PR84MB3787.NAMPRD84.PROD.OUTLOOK.COM
Backpatch-through: 19

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/03d03e62e69a61eb9b337d1915e0df8add31b5ee

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