Add atomic-counter to head.hackage

In light of ghc#23222 (closed), I believe we should also add atomic-counter to head.hackage.

changed the description

To be clear, do you want to add the atomic-counter library to head.hackage, or the atomic-counter benchmarks? The latter is much trickier.

I meant the benchmarks, since those currently segfault and that would be quite important to detect.

OK. I believe @mpickering knows all of the parts of the code that need to be changed to add benchmark runs to head.hackage (we do something similar for bytestring/containers/text), but I'm not sure if these steps are documented anywhere.

I made a MR to add the testsuite - !309

Thanks!

I'm confused. Wasn't the thing that triggered ghc#23222 (closed) the benchmark suite for atomic-counter, not the test suite? (We could still add the test suite, I suppose, but it's a separate thing entirely.)

mentioned in commit 521ddd29

mentioned in merge request !309