Fix the benchmarks for Julia 1.12

[MaxenceGollier]

@amontoison i investigated a bit, it seems that BenchmarkCI is just broken with Julia 1.12. Why don't we use PkgBenchmark.jl. Waiting for your opinion and then i will try to migrate.

[amontoison]

Can't we just run the benchmarks on Julia 1.11.7 or the LTS version?

I have my colleague Michael Saunders today and tomorrow in Chicago so can't have a look before Wesnesday.

We can do a quick zoom meeting / phone call if you want to sort this out.

[MaxenceGollier]

I am not in a hurry don't worry, I was just having a look at it.

Sure we could run them on the LTS version.

[amontoison]

Let's update the CI benchmarks to run them on the LTS version by default for now.