devops: run conda test builds on macos-13

Author: mxschmitt

.github/workflows/ci.yml

@@ -157,7 +157,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-20.04, macos-12, windows-2019]
+        os: [ubuntu-20.04, macos-13, windows-2019]
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v3