fix bundle requirement on keys and certs

Signed-off-by: Asra Ali <asraa@google.com>

cmd/cosign/cli/verify/verify_blob.go

@@ -170,7 +170,9 @@ func (c *VerifyBlobCmd) Exec(ctx context.Context, blobRef string) error {
 		if err != nil {
 			return err
 		}
-		if b.Cert == "" {
+		// A certificate is required in the bundle unless we specified with
+		//  --key, --sk, or --certificate.
+		if b.Cert == "" && co.SigVerifier == nil && cert == nil {
 			return fmt.Errorf("bundle does not contain cert for verification, please provide public key")
 		}
 		// b.Cert can either be a certificate or public key