ci: Pin macos to macos-13 for now

macos-latest now runs on Apple Silicon, which fails one test
and probably still needs extra work for the packaging to work.
Until that's figured out, run on macos-13.

.github/workflows/ci.yml

@@ -64,13 +64,13 @@ jobs:
               -Dvapoursynth=enabled
           - {
             name: macOS Debug,
-            os: macos-latest,
+            os: macos-13,
             buildtype: debugoptimized,
             args: -Ddefault_library=static -Dbuild_osx_bundle=true -Dlocal_boost=true --force-fallback-for=ffms2
           }
           - {
             name: macOS Release,
-            os: macos-latest,
+            os: macos-13,
             buildtype: release,
             args: -Ddefault_library=static -Dbuild_osx_bundle=true -Dlocal_boost=true --force-fallback-for=ffms2
           }
@@ -114,7 +114,7 @@ jobs:
           popd
 
       - name: Install dependencies (MacOS)
-        if: matrix.config.os == 'macos-latest'
+        if: startsWith(matrix.config.os, 'macos-')
         run: |
           export HOMEBREW_NO_INSTALL_CLEANUP=1
           export HOMEBREW_NO_INSTALLED_DEPENDENTS_CHECK=1
@@ -170,14 +170,14 @@ jobs:
       
       # macOS artifacts
       - name: Generate macOS installer
-        if: matrix.config.os == 'macos-latest'
+        if: startsWith(matrix.config.os, 'macos-')
         run: |
           meson compile osx-bundle -C build
           meson compile osx-build-dmg -C build
 
       - name: Upload artifacts - macOS dmg
         uses: actions/upload-artifact@v3
-        if: matrix.config.os == 'macos-latest'
+        if: startsWith(matrix.config.os, 'macos-')
         with:
           name: ${{ matrix.config.name }} - installer
           path: build/Aegisub-*.dmg