Revert to macos-latest as missing Python versions were added back

As described in actions/runner-images#9770, `macos-latest` was missing cached Python versions 3.9 and 3.10, forcing temporary use of `macos-13`. As the Python versions have been added, we can again use `macos-latest`.

.github/workflows/test-python-package.yml

@@ -17,7 +17,7 @@ on:
 jobs:
     build:
         name: Test on ${{ matrix.os }} with all supported Python versions
-        runs-on: ${{ format('{0}', matrix.os)  }} # "-latest" is added here so we can use OS in the format expected by CodeCov
+        runs-on: ${{ format('{0}-latest', matrix.os)  }} # "-latest" is added here so we can use OS in the format expected by CodeCov
 
         strategy:
             matrix: