chore(api): pin dependency poetry-core to ==1.8.1

Part-of: <https://dev.funkwhale.audio/funkwhale/funkwhale/-/merge_requests/2711>

api/pyproject.toml

@@ -128,7 +128,7 @@ django-extensions = "==3.2.3"
 typesense = ["typesense"]
 
 [build-system]
-requires = ["poetry-core>=1.0.0"]
+requires = ["poetry-core==1.8.1"]
 build-backend = "poetry.core.masonry.api"
 
 [tool.pylint.master]