GITHUB: bump CI macOS version to macos-latest

Signed-off-by: Stefan Westerfeld <stefan@space.twc.de>

.github/workflows/testing.yml

@@ -7,11 +7,11 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v3
-    - name: Test Build
+    - name: Test Linux Build
       run: misc/dbuild.sh
   macos:
-    runs-on: macos-11
+    runs-on: macos-latest
     steps:
     - uses: actions/checkout@v3
-    - name: Test Build
+    - name: Test macOS Build
       run: misc/macbuild.sh