home-assistant-component-tests: Reduce to two parallel test runners

The component tests are rather short, and each runner has a certain
setup cost. So we're better off, just starting fewer of them and have
them do more work.

It also works around a race condition, that upstream likely isn't
running into, because of the hardware specs¹ for the runners.

[1] https://docs.github.com/en/actions/using-github-hosted-runners/about-github-hosted-runners#supported-runners-and-hardware-resources

pkgs/servers/home-assistant/tests.nix

@@ -88,7 +88,7 @@ in lib.listToAttrs (map (component: lib.nameValuePair component (
     dontUsePytestXdist = true;
 
     pytestFlagsArray = lib.remove "tests" old.pytestFlagsArray
-      ++ [ "--numprocesses=4" ]
+      ++ [ "--numprocesses=2" ]
       ++ extraPytestFlagsArray.${component} or [ ]
       ++ [ "tests/components/${component}" ];