Verifies issue creation for a missing header in the signature base.
Issue reported: {
    issue : {
        code : SRIMessageSignatureIssue
        details : {
            sriMessageSignatureIssueDetails : {
                error : SignatureBaseMissingHeader
                integrityAssertions : [
                ]
                request : {
                    requestId : <string>
                    url : http://127.0.0.1:8000/inspector-protocol/resources/sri-message-signature-test.php?input=signature%3D%28%22unencoded-digest%22%3Bsf+%22x-test-header%22%29%3Bkeyid%3D%22JrQLj5P%2F89iXES9%2BvFgrIy29clF9CC%2FoPPsw3c5D0bs%3D%22%3Btag%3D%22sri%22&signature=signature%3D%3ASbCdPUyjc0IBJjFbVRWs81ucEUcFz87b37nQ63d6kDW%2B%2FJvDmET6O5cSdwlddePvlwemLdaWFuY6pQGO%2BhrkAg%3D%3D%3A&digest=sha-256%3D%3AX48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE%3D%3A
                }
                signatureBase :
            }
        }
    }
}