compile error on ubuntu 24.04

[alesof]

Hi there!

I'm using the library in a docker container with ubuntu 24.04 as base (which ships with gcc13). The deprecation of const-ref version of the method doNotOptimize in the google benchmark library makes compilation fail due to warnings being treated as errors.

The suggested way from google is to store data in a local variable and call doNotOptimize on that, avoiding undesired compiler optimizations (e.g. donotoptimize_test). I can open a PR with this solution.

[erenon]

Please do open a PR. Thanks!