_{tachometer-reporter-action v2 for CI}

On a semi-related note, the Tachometer comment will keep appearing for PRs against v10.x, even when it shouldn't, as there's no way at this time to get a reference to the target branch for workflow_run events when the workflow is triggered due to a PR from a fork. To get the reporter at least semi-working, it uses the SHA of the location in which the reporter is running, aka, main, to use as the base ref. This, however, has the effect of always reporting the JS changed as main and v10.x are now divergent so the diff between them is meaningless.

So it'll be a bit noisy and there will be some empty comments like above, but we'll still get reporting when the benches run, which seems preferable to disabling the thing on branches other than main.

I don't know what else to do here besides write a script to start querying GH's API manually which I'm not exactly thrilled about nor enthusiastic to do; feels like there's a really weird gap in the event payload data here. I opened a couple threads on their site-wide discussions repo, we'll see if that goes anywhere I guess.