need path to sed on macos 2

.github/workflows/dotnet-core.yml

@@ -43,6 +43,7 @@ jobs:
       run: |
           brew install gnu-sed
           PATH="/opt/homebrew/opt/gnu-sed/libexec/gnubin:$PATH"
+          sed --version
 
       # See https://github.com/microsoft/vstest/issues/2952 for why the --blame stuff below is needed.
       # Without it, the test runner crashes on ubuntu (but not Windows)/