build: switch to macos "large" to fix missing Firefox

The Arm64 images have been catered to Google and its Chrome browser
only, omitting Firefox.

Ref actions/runner-images#9974

Author: Krinkle

.github/workflows/CI.yaml

@@ -27,9 +27,9 @@ jobs:
             node: 20.x
 
           # Includes Firefox, Google Chrome, Safari
-          # https://github.com/actions/runner-images/blob/macos-15/20241217.493/images/macos/macos-15-Readme.md
+          # https://github.com/actions/runner-images/blob/macos-14/20241216.504/images/macos/macos-14-Readme.md
           - name: "macOS: Node 20"
-            os: macos-15
+            os: macos-14-large
             node: 20.x
 
     name: ${{ matrix.name }}