[CI] Build on macos-14 rather than macos-latest

In emsdk we actually build on macos-13, but sadly there is not macos-13
available in github actions.

Author: sbc100

.github/workflows/ci.yml

@@ -52,7 +52,10 @@ jobs:
     strategy:
       matrix:
         # Test on the oldest support Ubuntu version in addition to `latest`.
-        os: [ubuntu-22.04, ubuntu-latest, macos-latest, windows-latest, windows-11-arm]
+        # Build using the oldest support macOS version.  For emsdk this is
+        # currently macos-13, but unfortunately that doesn't exist in github
+        # actions so we settle for macos-14.
+        os: [ubuntu-22.04, ubuntu-latest, macos-14, windows-latest, windows-11-arm]
     steps:
     - uses: actions/setup-python@v5
       with:
@@ -74,7 +77,7 @@ jobs:
 
     - name: install ninja (macos)
       run: brew install ninja
-      if: matrix.os == 'macos-latest'
+      if: startsWith(matrix.os, 'macos')
 
     - name: install ninja (win)
       run: choco install ninja
@@ -94,7 +97,7 @@ jobs:
 
     - name: cmake (macos)
       run: cmake -S . -B out -G Ninja -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=out/install '-DCMAKE_OSX_ARCHITECTURES=x86_64;arm64'
-      if: matrix.os == 'macos-latest'
+      if: startsWith(matrix.os, 'macos')
 
     - name: cmake (win)
       # -G "Visual Studio 15 2017"