Bring in the python38 module for build

Nodejs requires at least python38 and jinja2 to build.
The python38 module has both available for use,
therefore we bring it in to build with.

This comes at a cost of no longer shipping ix86 arches due to python38
not shipping on those, so we cannot install them even as BuildRequire only.

Newer python streams do not ship with jinja2 we need to build Nodejs.

The only runtime requirement for python is coming from nodejs-packaging.
The package does not require newer python than distribution's default
Python 3.6, so we do not require the python38 module for the module's runtime.

Related: RHEL-35991

nodejs.yaml

@@ -16,6 +16,8 @@ data:
   configurations:
   - context: rhel8
     platform: el8
+    buildrequires:
+      python38: [ '3.8' ]
     buildopts:
       rpms:
         macros: |