testing/check_software: add libanl in system libraries whitelist

libanl is part of glibc since 2001 (see
https://sourceware.org/git/?p=glibc.git;a=blob;f=ChangeLog.old/ChangeLog.12;h=adcf9081d44c06e03c3899612afba7c8c0d9b3fa;hb=HEAD#l5595)

See merge request nexedi/slapos.core!291