moodle-report_usergrades/db/access.php

<?php

$capabilities = array(
    'report/usergrades:view' => array(
        'riskbitmask' => RISK_PERSONAL,
        'captype' => 'read',
        'contextlevel' => CONTEXT_SYSTEM,
        'archetypes' => array(
            'manager' => CAP_ALLOW,
        ),
    ),
);