Update stubs to match signature of actual methods

[SpangleLabs]

#2526 has broken building v5.32.2 with the containers_image_fulcio_stub and containers_image_rekor_stub build tags, as the signatures for verifyRekorFulcio() and VerifyRekorSET() were updated without updating the corresponding stubs.

This PR updates the stubs to match

[mtrmac]

Thanks!

First, https://github.com/containers/image/blob/main/CONTRIBUTING.md#sign-your-prs please, we can’t really even look at contributions with unclear copyright status.