gnuradio.unwrapped: Add pythonRuntime deps only with python-support

Especially useful when cross compiling and when enabling gr-filter
feature, which has the following in upstream's CMakeLists.txt file:

```
gr_python_check_module_raw("pyqtgraph" "import pyqtgraph" PYQTGRAPH_FOUND)
gr_python_check_module_raw("scipy" "import scipy" SCIPY_FOUND)

if(NOT PYQTGRAPH_FOUND OR NOT SCIPY_FOUND)
message(WARNING "PyQtGraph and Scipy are required to run the filter design tool, "
"but are not detected! Please make sure they are installed on "
"the target system.")
endif(NOT PYQTGRAPH_FOUND OR NOT SCIPY_FOUND)

if(ENABLE_PYTHON)
add_subdirectory(python/filter)
add_subdirectory(python/filter/design)
add_subdirectory(python/filter/gui)
add_subdirectory(apps)
if(ENABLE_EXAMPLES)
add_subdirectory(examples)
endif(ENABLE_EXAMPLES)
endif(ENABLE_PYTHON)
if(ENABLE_GRC)
add_subdirectory(grc)
endif(ENABLE_GRC)
```

pkgs/applications/radio/gnuradio/shared.nix

···
       feat: info:
       (lib.optionals (hasFeature feat) (
         (lib.optionals (builtins.hasAttr "runtime" info) info.runtime)
-        ++ (lib.optionals (builtins.hasAttr "pythonRuntime" info) info.pythonRuntime)
+        ++ (lib.optionals (
+          builtins.hasAttr "pythonRuntime" info && hasFeature "python-support"
+        ) info.pythonRuntime)
       ))
     ) featuresInfo
   );