JSON_ARRAYAGG + JSON_TABLE + GROUP BY charset issue

I am seeing a charset edge case under a very specific set of circumstances.

Related: https://jira.mariadb.org/browse/MDEV-24784 (I can reproduce this bug in server 11.4.8, which is higher than than the versions marked as "fixed" in this issue.)

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I have minified the test case so it works in a single SELECT statement without creating tables.

1. Test case

SELECT

    JSON_VALUE(JSON_ARRAYAGG('×'), "$[0]") AS working,

    JSON_EXTRACT(JSON_ARRAYAGG('×'), "$[0]") AS broken,

    JSON_ARRAYAGG('×') AS also_broken

FROM information_schema.engines,

     JSON_TABLE(1, '$' COLUMNS (x FOR ORDINALITY)) j

GROUP BY engine

LIMIT 1;

1. Expected outcome

1. Column one shows something
2. Column two shows the column one thing enclosed in double quotation marks
3. Column three shows the column one thing enclosed in square brackets

1. Actual outcome

   1. `×` ✅

   2. `"?"` ❌

   3. `["?"]` ❌