tests/lint: ensure initialization does not modify shared type

In my not yet published rewrite of lint's init.c, I forgot to copy the
array type. Guard against this bug, which would have been hard to find.

Given that in C, the declaration 'int a[], b[]' creates two different
type objects anyway, it's not easy to come up with a test case that
actually triggers this possible bug.  I'm not sure whether this test
indeed catches this bug.  If not, I'll add another test.

(rillig)