Fix batch validation when there are only warnings

[tylerjmchugh]

Currently if you run batch validation on a selection of records with only validation warnings the UI and json response is incorrect:

{  
    "uuid": "e02c689f-202a-450b-bbdf-32cebe2f4845",  
    "metadata": [  
        201646  
    ],  
    "validMetadata": {},  
    "invalidMetadata": {  
        "201646": {  
            "message": "Is invalid",  
            "uuid": "3cc1c921-152b-4b8f-81b4-ebb1b13a3f53",  
            "draft": false,  
            "approved": true,  
            "date": "2026-02-03T12:47:19.861402Z"  
        }  
    },  
    "metadataWithWarnings": {  
        "201646": {  
            "message": "Has warnings",  
            "uuid": "3cc1c921-152b-4b8f-81b4-ebb1b13a3f53",  
            "draft": false,  
            "approved": true,  
            "date": "2026-02-03T12:47:19.857906Z"  
        }  
    },  
    "validationErrors": {},  
    "validationWarnings": {  
        "201646": [  
            {  
                "schematron": "schematron-rules-resource-content",  
                "messages": {  
                    "sample.pdf": [  
                        "Content must either be tagged as structural content or explicitly marked as an artifact so assistive technology can skip it"  
                    ]  
                }  
            }  
        ]  
    },  
    "numberOfRecords": 1,  
    "numberOfRecordsProcessed": 1,  
    "numberOfValidRecords": 0,  
    "numberOfInvalidRecords": 1,  
    "numberOfRecordsWithValidationWarnings": 1,  
    "numberOfNullRecords": 0,  
    "numberOfRecordsNotEditable": 0,  
    "startIsoDateTime": "2026-02-03T12:47:18.3719Z",  
    "endIsoDateTime": "2026-02-03T12:47:20.376935Z",  
    "ellapsedTimeInSeconds": 2,  
    "totalTimeInSeconds": 2,  
    "running": false,  
    "type": "MetadataValidationProcessingReport"  
}

This occurs because the current isValid property is set to true if any schematron (even report only schematrons) has failed asserts.

This PR aims to fix this issue by correctly setting the record as valid when there are only warnings.

Checklist

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