pyproject: It's tool.zest-releaser, not tools.zest-releaser.

https://zestreleaser.readthedocs.io/en/latest/options.html

Author: jamadden

pyproject.toml

@@ -65,6 +65,6 @@ test = [
 [tool.setuptools.dynamic]
 version = {attr = "greenlet.__version__"}
 
-[tools.zest-releaser]
+[tool.zest-releaser]
 python-file-with-version = "src/greenlet/__init__.py"
 create-wheel = false