Update fixture to match civi core version of tcpdf
Core upgraded tcpdf at https://github.com/civicrm/civicrm-core/pull/20540#issuecomment-856908288 which I knew and had r-run
with cdntax, but at the time it was still marking it as 6.3.5 even with the version change: https://github.com/civicrm/civicrm-core/pull/20540#issuecomment-857061781
This marks it 6.4.2.