Work around DBIx::Class leak test bug for users of SQLA based DBIC

Work around DBIx::Class leak test bug for users of SQLA based DBIC

t/52leaks.t mistakenly treats non-closure anon sub declarations (which perl
caches in the optree) as a leak; introducing a spurious but minimally
invasive lexical makes them into closures and works around this.

Since people are considering testing SQLA against DBIx::Class via downgrading
to the last release before the hostile fork of SQLA::Classic and that release
is set in stone, this seems like the least horribad way to still pass the
DBIC t/ and xt/ test suites.