Update macOS version in CI workflow

macos-13 will be removed and macos-15 seems to be slow: actions/runner-images#12545

Author: chrjohn

.github/workflows/maven.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [ubuntu-latest, macOS-13]
+        os: [ubuntu-latest, macOS-14]
         java: [8, 11, 21]
       fail-fast: false
       max-parallel: 4