poetry: restore poetry-core override

pkgs/tools/package-management/poetry/default.nix

@@ -1,9 +1,25 @@
-{ python3 }:
+{ python3, fetchFromGitHub }:
 
 let
   python = python3.override {
-    packageOverrides = self: super: {
+    packageOverrides = self: super: rec {
       poetry = self.callPackage ./unwrapped.nix { };
+
+      # The versions of Poetry and poetry-core need to match exactly,
+      # and poetry-core in nixpkgs requires a staging cycle to be updated,
+      # so apply an override here.
+      #
+      # We keep the override around even when the versions match, as
+      # it's likely to become relevant again after the next Poetry update.
+      poetry-core = super.poetry-core.overridePythonAttrs (old: rec {
+        version = poetry.version;
+        src = fetchFromGitHub {
+          owner = "python-poetry";
+          repo = "poetry-core";
+          rev = version;
+          hash = "sha256-OfY2zc+5CgOrgbiPVnvMdT4h1S7Aek8S7iThl6azmsk=";
+        };
+      });
     } // (plugins self);
   };