Fix shebang of installed python scripts

Closes: https://github.com/NixOS/nixpkgs/pull/449340
Fixes: https://github.com/NixOS/nixpkgs/issues/449325

pkgs/development/interpreters/python/hooks/default.nix

@@ -138,6 +138,7 @@ in
           propagatedBuildInputs = [ installer ];
           substitutions = {
             inherit pythonInterpreter pythonSitePackages;
+            python = python.interpreter;
           };
         } ./pypa-install-hook.sh
       )

pkgs/development/interpreters/python/hooks/pypa-install-hook.sh

@@ -8,7 +8,7 @@ pypaInstallPhase() {
     pushd dist >/dev/null
 
     for wheel in *.whl; do
-        @pythonInterpreter@ -m installer --prefix "$out" "$wheel"
+        @pythonInterpreter@ -m installer --prefix "$out" --executable "@python@" "$wheel"
         echo "Successfully installed $wheel"
     done