Update the macOS CI runner

Version 12 is no longer available.

Author: s3rvac

.github/workflows/tests.yml

@@ -6,7 +6,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-22.04, macos-12, windows-2022]
+        os: [ubuntu-22.04, macos-13, windows-2022]
         python-version: [3.8, 3.11, pypy-2.7, pypy-3.8]
     steps:
       - uses: actions/checkout@v4