Error on OCI style repositories

Seeing the following error when version-checker attempts to check the fluent-bit repository:

```
time="2023-10-16T21:36:44Z" level=error msg="cr.fluentbit.io/v2/fluent/fluent-bit/manifests/2.0: failed to get manifest response for tag, skipping (404): {\"errors\":[{\"code\":\"MANIFEST_UNKNOWN\",\"message\":\"OCI index found, but accept header does not support OCI indexes\"}]}\n" client=

time="2023-10-16T21:40:19Z" level=error msg="cr.fluentbit.io/v2/fluent/fluent-bit/manifests/sha256-9b386368a776f8f8a25ee7113ef8f39ae9004d3b6e8a80d0848bd9e37a9c6aae.sig: failed to get manifest response for tag, skipping (404): {\"errors\":[{\"code\":\"MANIFEST_UNKNOWN\",\"message\":\"OCI manifest found, but accept header does not support OCI manifests\"}]}\n" client=
```

Image of the container is `cr.fluentbit.io/fluent/fluent-bit:2.1.9`

Start by reproducing the failure with the cr.fluentbit.io/fluent/fluent-bit:2.1.9 image and inspect how version-checker handles its manifest responses. Trace the image registry request path and verify that OCI indexes and manifests are accepted without the reported errors.

Written by the indexing model from the issue text.