exec: mismatched batch width and schema length on fakedist config

[yuzefovich]

I added the following configs to logic.go:

{name: "fakedist-vec", numNodes: 3, useFakeSpanResolver: true, overrideDistSQLMode: "on", overrideOptimizerMode: "off", overrideExpVectorize: "on"},
{name: "fakedist-opt-vec", numNodes: 3, useFakeSpanResolver: true, overrideDistSQLMode: "on", overrideOptimizerMode: "on", overrideAutoStats: "false", overrideExpVectorize: "on"},

and the following logic test fails on master:

# LogicTest: fakedist-vec fakedist-opt-vec

statement ok
CREATE TABLE abc (a INT PRIMARY KEY, b INT, c INT)

statement ok
INSERT INTO abc VALUES (1, 2, 3)

query I colnames
SELECT a+b+c AS foo FROM abc
----
foo
6

Note that it fails pretty reliably, but sometimes it's either of the configs, sometimes it's both (I haven't seen it succeed in 10 or so runs).

[yuzefovich]

Assigning to @asubiotto since you expressed an interest in this issue in #38920.