yapf test leaves a stray process that never quits

[nagisa]

I ran the test suite just test-ci a boatload of times on my machine.

Now I have a bunch of yapf processes that are idling with no apparent intent of quitting:

$ ps aux | grep yapf | wc -l
72
$ ps aux | grep -- '-m yapf' | tail -n1
nagisa   2230648  0.0  0.0  29836 17004 ?        S    02:43   0:00 /nix/store/l8d6q4y9cvp2d5qf2sxxj072668bfcjr-python3-3.10.13/bin/python3.10 -m yapf -pdr pytest scripts debug_scripts /somewhere/nearcore