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_12_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/94246405d5d7cb90fc2eff12d9c42b38070fb970

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