pgsql: pageinspect: Fix memory context allocation of page in brin_revma

pageinspect: Fix memory context allocation of page in brin_revmap_data()

This caused the function to fail, as the aligned copy of the raw page
given by the function caller was not saved in the correct memory
context, which needs to be multi_call_memory_ctx in this case.

Issue introduced by 076f4d9.

Per buildfarm members sifika, mylodon and longfin.  I have reproduced
that locally with macos.

Discussion: https://postgr.es/m/YjFPOtfCW6yLXUeM@paquier.xyz
Backpatch-through: 10

Branch
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REL_14_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/dc5b3bdae31690e11839079e15b74ba0df0aa167

Modified Files
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contrib/pageinspect/brinfuncs.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)