In the commit mentioned at the end, a new variable was added
conditionally:

```yml
   # If post build signing, then OSX and Linux don't publish during their main pass. Otherwise, always publish
   - ${{ if eq(variables['PostBuildSign'], 'true') }}:
     - name: _NonWindowsInternalPublishArg
       value: -publish
```

.. but this resulted in the variable not getting defined at all in the
final yaml. I think the reason is that you can't define a variable based
on a the value of another variable, at yaml expansion time. So, access
the variable at run time.

```
commit b36ce43
Author: Matt Mitchell <mmitche@microsoft.com>
Date:   Fri Aug 5 14:05:37 2022 -0700

    Add support for in-build signing (dotnet#164)
```