GITHUB: test on macos-13, too

Signed-off-by: Stefan Westerfeld <[email protected]>

Author: swesterfeld

Diff for: .github/workflows/testing.yml

@@ -15,3 +15,9 @@ jobs:
     - uses: actions/checkout@v3
     - name: Test macOS Build
       run: misc/macbuild.sh
+  macos-13:
+    runs-on: macos-13
+    steps:
+    - uses: actions/checkout@v3
+    - name: Test macOS Build
+      run: misc/macbuild.sh