Speed up tests

Maybe also setting _PHPUNIT_CONCURRENT could help.

I was just looking for that setting, but you beat me to it.

That cut 25 minutes off of the tests!

Head is still failing tests I think. I'm not sure if we want to merge this in, or just manually port it to the other issue since tests are passing there.

6.3.x is currently passing except for the "next major" tests. This suggests that _PHPUNIT_CONCURRENT is causing the failure.