Mark program file as inline source for consistency

Thanks to @webknjaz for the style pointer.

Co-authored-by: Sviatoslav Sydorenko <wk.cvs.github@sydorenko.org.ua>

Author: ajnelson-nist

source/guides/single-sourcing-package-version.rst

@@ -50,7 +50,7 @@ number of your project:
        the package's dependencies.
 
        Also, please be aware that declarative config indicators, including the
-       ``attr:`` directive, are not supported in parameters to setup.py.
+       ``attr:`` directive, are not supported in parameters to ``setup.py``.
 
 #.  Use an external build tool that either manages updating both locations, or
     offers an API that both locations can use.