main.star: adjust LUCI load at openbsd-ppc64 builder

Try setting GOMAXPROCS. We'll start with 2 to confirm a
clear effect, then may raise it to 4.

For golang/go#70213

Change-Id: Ic5f5e0b99c5e9ead896a465e39286ab161f431c7
Reviewed-on: https://go-review.googlesource.com/c/build/+/625317
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>

main.star

@@ -1511,6 +1511,10 @@ def define_builder(env, project, go_branch_short, builder_type):
     if builder_type == "linux-arm":
         base_props["env"]["GOARM"] = "6"
 
+    # TODO(go.dev/issue/70213): Throttle back the load average.
+    if builder_type == "openbsd-ppc64":
+        base_props["env"]["GOMAXPROCS"] = "2"
+
     # Construct the basic dimensions for the build/test running part of the build.
     #
     # Note that these should generally live in the worker pools.