Update pyproject.toml

Author: NiklasRosenstein

pyproject.toml

@@ -1,7 +1,7 @@
 [build-system]
 # NOTE(NiklasRosenstein): We pin this version so we can keep using the old way that Slap supports installing
 #                         the "docs" extra without Poetry complaining about invalid format of the requirements.
-requires = ["poetry-core>=1.1.0"]
+requires = ["poetry-core>=1.1.0a6"]
 build-backend = "poetry.core.masonry.api"
 
 [tool.poetry]