Fix test suite check annotations

[tmpduarte]

The test suite is showing a warning that are then shown in the pull requests:

[frm]

This is because the TestPolicy exists only for assertions. We can silence this by defining a basic can?/3 that returns always true, I think /cc @naps62

[naps62]

Yes. That sounds like a good idea

Either that, or define the opposite on the policy itself. e.g.: a __before_compile__ call that would define def can?(_, _, _), do: false, meaning that any policy where the user forgets to explicitly define permissions, would falback to disallowing everything, which I believe is safer than the opposite