treewide: *Flags convert to list from str

*Flags implies a list

slightly relevant:
> stdenv: start deprecating non-list configureFlags https://github.com/NixOS/nixpkgs/pull/173172

the makeInstalledTests function in `nixos/tests/installed-tests/default.nix` isn't available outside of nixpkgs so
it's not a breaking change

pkgs/development/python-modules/python-openems/default.nix

@@ -36,7 +36,7 @@ buildPythonPackage rec {
     h5py
   ];
 
-  setupPyBuildFlags = "-I${openems}/include -L${openems}/lib -R${openems}/lib";
+  setupPyBuildFlags = [ "-I${openems}/include" "-L${openems}/lib" "-R${openems}/lib" ];
   pythonImportsCheck = [ "openEMS" ];
 
   meta = with lib; {