fix(go): prevent running with valgrind

[not-matthias]

Works now as expected:

> codspeed run --skip-upload -- go test -bench=.                                             nix-shell-env 
Unofficially supported system: nixos 25.05. Continuing with best effort support.

►►► Preparing the environment 
Valgrind is already installed with the correct version, skipping installation
Environment ready

►►► Running the benchmarks 
WARNING: Go benchmarks can only be run with walltime
Error: failed to execute the benchmark process, exit code: 1