fix: to_columns must be an array

[mnahkies]

What are you changing in this pull request and why?

when providing a single column as a string, instead of an array, the compiled sql ends up like this:

some_id bigint not null references "database"."schema"."table" (e, x, t, e, r, n, a, l, _, i, d),

adjust the example to show an array with a single element instead.

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[mirnawong1]

hey @mnahkies great catch and thanks so much for opening this pr up to add this! you're absolutely right, going to merge this for you!