Update passport-saml tests (#44865)
Update passport-saml tests (#44865)

fs.readFileSync requires lowercase 'utf8', not "UTF8", and node types
now enforce that. I updated passport-saml tests to match.
dsebastien/DefinitelyTyped,georgemarshall/DefinitelyTyped,georgemarshall/DefinitelyTyped,markogresak/DefinitelyTyped,georgemarshall/DefinitelyTyped,mcliment/DefinitelyTyped,dsebastien/DefinitelyTyped,georgemarshall/DefinitelyTyped