pgsql: Fix the volatility setting of json{b}_strip_nulls

Fix the volatility setting of json{b}_strip_nulls

Commit 4603903d294 unfortunately reset the volatility of these functions
to STABLE whereas they had previously been set to IMMUTABLE. We can't
force a catalog update in the stable release, although a pg_update would
probably do the trick. A simpler fix, though, for affected users is
probably a simple catalog surgery along the lines of:

UPDATE pg_proc SET provolatile = 'i' WHERE oid in (3261,3262);

Applied to 18 only. In master we are planning to get rid of the separate
redeclarations for defaults in system_functions.sql.

Bug: #19409
Reported-By: Lucio Chiessi <lucio(dot)chiessi(at)trustly(dot)com>
Discussion: https://postgr.es/m/19409-e16cd2605e59a4af@postgresql.org

Branch
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REL_18_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/2f6ee7b389c2b570ac55eb25273872b729d397c8

Modified Files
--------------
src/backend/catalog/system_functions.sql | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)