Update the RHCOS 4.21 bootimage metadata to 9.6.20251023-0

The changes done here will update the RHCOS 4.21 bootimage metadata and
address the following issues:

OCPBUGS-62699: Revert inclusion of AWS ECR credential provider in RHEL layer

This change was generated using:

```
plume cosa2stream --target data/data/coreos/rhcos.json \
    --distro rhcos --no-signatures --name rhel-9.6 \
    --url https://rhcos.mirror.openshift.com/art/storage/prod/streams \
    x86_64=9.6.20251023-0        \
    aarch64=9.6.20251023-0       \
    s390x=9.6.20251023-0         \
    ppc64le=9.6.20251023-0
```

Author: mike-nguyen