Changed GitHub test-coverage workflow to run on mac

The default in test-coverage.yaml is to run the test coverage on ubuntu-latest, but the package fails on ubuntu with an error about the RcppZiggurat.

"Error in `dyn.load(file, DLLpath = DLLpath, ...)`: unable to load shared object '/home/runner/work/_temp/Library/RcppZiggurat/libs/RcppZiggurat.so':
  libgsl.so.27: cannot open shared object file: No such file or directory"

Changed test-coverage.yaml to run on macos-latest

.github/workflows/test-coverage.yaml

@@ -11,7 +11,7 @@ permissions: read-all
 
 jobs:
   test-coverage:
-    runs-on: ubuntu-latest
+    runs-on: macos-latest
     env:
       GITHUB_PAT: ${{ secrets.GITHUB_TOKEN }}