FIX? channel prefix in r slope

[mathurinm]

possible fix for https://github.com/benchopt/benchmark_slope/actions/runs/15015137872/job/42191199000#step:7:510

see https://benchopt.github.io/whats_new.html#api

[jolars]

Hm, but I think it's the release that's erroring out, and not the development version, so this shouldn't be the issue, right?

[jolars]

I opened this issue over in the benchmark_template repo: benchopt/template_benchmark#43

I think the error is "The following argument was not expected: --update-all"

[jolars]

Do I understand it correctly that this does not work in the current benchopt release? (E.g. we cannot merge right now.)