governors advice may be obsolete in linuxtips.md about benchmarktools.jl

[vchuravy]

One of the issues is that frequency scaling introduces variance into the system. If your question is "how fast is this code running on my system", that doesn't matter as much.
But one of the core usages is to compare different benchmarks with each other and to do that reliably reducing variance is important. So I think the advise is generally still valid.