[4.10] boot sequence override request fails with Base.1.8.PropertyNotWritable on Lenovo SE450

This issue was identified once the initial problem in https://bugzilla.redhat.com/show_bug.cgi?id=2103710 was fixed (eTag issue was preventing this from happening).

While attempting to provision Lenovo SE450 machines, this error occurs:

{
  "error": {
    "code": "Base.1.8.GeneralError",
    "@Message.ExtendedInfo": [
      {
        "MessageArgs": [
          "BootSourceOverrideEnabled"
        ],
        "Resolution": "Remove the property from the request body and resubmit the request if the operation failed.",
        "MessageId": "Base.1.8.PropertyNotWritable",
        "Message": "The property BootSourceOverrideEnabled is a read only property and cannot be assigned a value.",
        "@odata.type": "#Message.v1_1_0.Message",
        "MessageSeverity": "Warning"
      }
    ],
    "message": "A general error has occurred. See ExtendedInfo for more information."
  }
}

This is triggered by the fact that the server provides /redfish/v1/Systems/1/Pending SettingsURI however this URI does not allow setting BootSourceOverrideEnabled which sushy expects.

This may be a problem in sushy or in the BMC - at this stage it isn't clear.

The goal of this bug is to work around or resolve this issue.

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