ci: Don't run tests on macos-13

macos-13 runner is no longer supported.

Author: sjanc

.github/workflows/newt_test_all.yml

@@ -27,7 +27,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-latest, macos-13]
+        os: [ubuntu-latest]
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v3