Benchmarks no longer running

[hughsimpson]

For the move to GitHub actions, benchmarks were excluded. They should be included. Preferably in a manner that ensures a decent level of consistency on the runs - current target is not rerunning one every pull request but with an acceptance that that will sometimes be necessary. A good path to permitting improved results should be established, and scala 2/scala 3 comparison metrics should be established, instead of expecting them to be the same speed for the same thing all the time...