workflows: switch back to macos-latest

It's now an alias for macos-14.  Switch back so we get future OS
updates.

Author: bgilbert

.github/workflows/run_unit_tests.yml

@@ -16,7 +16,7 @@ jobs:
         include:
           - os: ubuntu-latest
             cc: gcc
-          - os: macos-14
+          - os: macos-latest
             cc: clang
           - os: windows-latest
             cc: clang