tools: increase macOS cores to 3 on GitHub CI

In efbec85, we reduced the cores to 2
based on GitHub documentation. The documentation now says that there are
3 cores.

Refs: https://docs.github.com/en/actions/using-github-hosted-runners/about-github-hosted-runners#supported-runners-and-hardware-resources
PR-URL: #45340
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>

.github/workflows/test-macos.yml

@@ -52,12 +52,12 @@ jobs:
       # The `npm ci` for this step fails a lot as part of the Test step. Run it
       # now so that we don't have to wait 2 hours for the Build step to pass
       # first before that failure happens. (And if there's something about
-      # `make run-ci -j2` that is causing the failure and the failure doesn't
+      # `make run-ci -j3` that is causing the failure and the failure doesn't
       # happen anymore running this step here first, that's also useful
       # information.)
       - name: tools/doc/node_modules workaround
         run: make tools/doc/node_modules
       - name: Build
-        run: make build-ci -j2 V=1 CONFIG_FLAGS="--error-on-warn"
+        run: make build-ci -j3 V=1 CONFIG_FLAGS="--error-on-warn"
       - name: Test
-        run: make run-ci -j2 V=1 TEST_CI_ARGS="-p actions --measure-flakiness 9"
+        run: make run-ci -j3 V=1 TEST_CI_ARGS="-p actions --measure-flakiness 9"