/etc/logcheck/ignore.d.server/nfs is in logcheck-database 1.3.17.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | ^\w{3} [ :0-9]{11} [._[:alnum:]-]+ rpc\.mountd: authenticated (un|)mount request from [._[:alnum:]-]+:[0-9]+ for (/[._[:alnum:]-]*)+ \((/[._[:alnum:]-]*)+\)$
^\w{3} [ :0-9]{11} [._[:alnum:]-]+ mountd\[[0-9]+\]: authenticated (un|)mount request from [._[:alnum:]-]+:[0-9]+ for (/[._[:alnum:]-]*)+ \((/[._[:alnum:]-]*)+\)$
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