build: test macos-13 on GitHub actions

We are in the process of updating macOS to version 13 in the
Jenkins CI, but unfortunately this is taking longer than expected.
Add it to the GitHub actions test matrix so that we have some coverage.

Refs: nodejs/build#3686

.github/workflows/test-macos.yml

@@ -38,7 +38,11 @@ permissions:
 jobs:
   test-macOS:
     if: github.event.pull_request.draft == false
-    runs-on: macos-14
+    strategy:
+      fail-fast: false
+      matrix:
+        macos-version: [macos-13, macos-14]
+    runs-on: ${{ matrix.macos-version }}
     env:
       CC: sccache gcc
       CXX: sccache g++