nixops_unstable: set Python interpreter to python39

The package encounters a build error when building with Python 3.10 due to
API breakage (collections.MutableMapping -> collections.abc.MutableMapping).

pkgs/applications/networking/cluster/nixops/default.nix

@@ -10,6 +10,7 @@ let
   interpreter = (
     poetry2nix.mkPoetryPackages {
       projectDir = ./.;
+      python = pkgs.python39;
       overrides = [
         poetry2nix.defaultPoetryOverrides
         (import ./poetry-git-overlay.nix { inherit pkgs; })

pkgs/applications/networking/cluster/nixops/pyproject.toml

@@ -5,7 +5,7 @@ description = "NixOps 2.0"
 authors = ["Adam Hoese <adam.hose@tweag.io>"]
 
 [tool.poetry.dependencies]
-python = "^3.8"
+python = "^3.9"
 nixops = {git = "https://github.com/NixOS/nixops.git"}
 nixops-aws = {git = "https://github.com/NixOS/nixops-aws.git"}
 nixops-digitalocean = {git = "https://github.com/nix-community/nixops-digitalocean.git"}

pkgs/applications/networking/cluster/nixops/shell.nix

@@ -5,6 +5,6 @@ pkgs.mkShell {
     pkgs.poetry2nix.cli
     pkgs.pkg-config
     pkgs.libvirt
-    pkgs.poetry
+    pkgs.python39Packages.poetry
   ];
 }