Use macOS 13 for unit tests instead of macOS 11 (#2912)

- macOS 11 is deprecated per https://github.com/actions/runner-images as
  of this commit

Author: moleske

.github/workflows/tests-unit.yml

@@ -52,7 +52,7 @@ jobs:
           - ubuntu-latest
           - ubuntu-20.04
           - macos-latest
-          - macos-11
+          - macos-13
     runs-on: ${{ matrix.os }}
     steps: