Affected: Go: github.com/sigstore/cosign/v3, Go: github.com/sigstore/cosign/v2

### Impact

A Cosign bundle can be crafted to successfully verify an artifact even if the embedded Rekor entry does not reference the artifact's digest, signature or public key. When verifying a Rekor entry, Cosign verifies the Rekor entry signature, and also compares the artifact's digest, the user's public key from either a Fulcio certificate or provided by the user, and the artifact signature to the Rekor entry contents. Without these comparisons, Cosign would accept any response from Rekor as valid. A malicious actor that has compromised a user's identity or signing key could construct a valid Cosign bundle by including any arbitrary Rekor entry, thus preventing the user from being able to audit the signing event.

This vulnerability only affects users that provide a trusted root via `--trusted-root` or when fetched automatically from a TUF repository, when no trusted key material is provided via `SIGSTORE_REKOR_PUBLIC_KEY`. When using the default flag values in Cosign v3 to sign and verify (`--use-signing-config=true` and `--new-bundle-format=true` for signing, `--new-bundle-format=true` for verification), users are unaffected. Cosign v2 users are affected using the default flag values.

This issue had previously been fixed in https://github.com/sigstore/cosign/security/advisories/GHSA-8gw7-4j42-w388 but recent refactoring caused a regression. We have added testing to prevent a future regression.

#### Steps to Reproduce

``` echo blob > /tmp/blob cosign sign-blob -y --…