pgsql: Fix incorrectly reported stats kind in "can't happen" ERROR

Fix incorrectly reported stats kind in "can't happen" ERROR

The error message(s) were reporting the stats kind of 'f', which is not
correct as that's for the "dependencies" statistics kind.

Reported-by: Horst Reiterer
Reviewed-by: Richard Guo
Discussion: https://postgr.es/m/18375-ba99383eb9062d6a@postgresql.org
Backpatch-through: 12, where MCV extended stats were added.

Branch
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REL_13_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/421dfb41a843a60c8cf4468e8c2328a24f390a90

Modified Files
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src/backend/statistics/mcv.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)