github workflows: separate jobs per runner

.github/workflows/pioneer-pr.yml

@@ -1,10 +1,28 @@
-name: Pioneer-PR
+name: Pioneer
 on: [pull_request, push]
 
 jobs:
-  pioneer_build_code:
-    name: Pioneer Build Code
-    runs-on: [ubuntu-latest, macos-latest]
+  pioneer_build_code_ubuntu:
+    name: (Ubuntu) Build Code
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        node-version: [12.x]
+    steps:
+    - uses: actions/checkout@v1
+    - name: Use Node.js ${{ matrix.node-version }}
+      uses: actions/setup-node@v1
+      with:
+        node-version: ${{ matrix.node-version }}
+    - name: build
+      run: |
+        yarn install --frozen-lockfile
+        yarn workspace pioneer run build:code
+
+jobs:
+  pioneer_build_code_osx:
+    name: (MacOS) Build Code
+    runs-on: macos-latest
     strategy:
       matrix:
         node-version: [12.x]