Use poetry-core as build backend

The poetry build backend was split into the package poetry-core.

See also
https://python-poetry.org/docs/pyproject/#poetry-and-pep-517
NixOS/nixpkgs#103325

Author: erictapen

pyproject.toml

@@ -1,6 +1,6 @@
 [build-system]
-requires = ["poetry>=1.0.0"]
-build-backend = "poetry.masonry.api"
+requires = ["poetry-core>=1.0.0"]
+build-backend = "poetry.core.masonry.api"
 
 [tool]
 [tool.poetry]