OCPBUGS-60949: Update the RHCOS 4.20 bootimage metadata

The changes done here will update the RHCOS 4.20 bootimage metadata and
address the following issues:

OCPBUGS-60664 - [4.19] linux-firmware updates required for GNR-D hardware

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=9.6.20250826-1                                    \
    aarch64=9.6.20250826-1                                   \
    s390x=9.6.20250826-1                                     \
    ppc64le=9.6.20250826-1
```

Author: aaradhak