poetry: Fix build with Python 3.8

pkgs/development/tools/poetry/default.nix

@@ -8,6 +8,12 @@ poetry2nix.mkPoetryApplication {
   pyproject = ./pyproject.toml;
   poetrylock = ./poetry.lock;
 
+  overrides = [ (poetry2nix.defaultPoetryOverrides.overrideOverlay (self: super: {
+    # Needed because poetry2nix currently doesn't handle pyproject.toml python bounds
+    # See https://github.com/nix-community/poetry2nix/issues/50
+    importlib-metadata = if python.pythonOlder "3.8" then super.importlib-metadata else null;
+  }))];
+
   src = fetchFromGitHub (lib.importJSON ./src.json);
 
   # "Vendor" dependencies (for build-system support)