Run Firefox and Chrome tests on Mac.

It turns out the Chrome team didn't test the new Chrome/Chromedriver 115
setup so I guess it's best we do it for them.

#1968

.github/workflows/mac.yml

@@ -0,0 +1,34 @@
+name: OSX Chrome and Firefox
+on:
+  push:
+    branches:
+    - main
+  pull_request:
+    branches:
+    - main
+jobs:
+  build:
+    runs-on: macos-13
+    timeout-minutes: 30
+    steps:
+    - uses: actions/checkout@v3
+    - name: Use Node.js
+      uses: actions/setup-node@v3
+      with:
+        node-version: '18.x'
+    - name: Install browsertime
+      run: npm ci
+    - name: Install python
+      uses: actions/setup-python@v4
+      with:
+        python-version: '3.11' 
+    - name: Install dependencies
+      run: |
+        brew update
+        brew install google-chrome
+        brew install --cask firefox
+    - name: Test Chrome 
+      run: ./bin/browsertime.js -b chrome -n 1 https://www.sitespeed.io/
+    - name: Test Firefox
+      run: ./bin/browsertime.js -b firefox -n 1 https://www.sitespeed.io/
+