/usr/share/cups/templates/classes-header.tmpl is in cups-server-common 2.2.7-1ubuntu2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 | <P ALIGN="CENTER">{total=0?No classes:Showing {#printer_name} of {total} class{total=1?:es}}.</P>
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