Specify the directory to use for the package in pyproject.toml.

setuptools attempts to discern what directories need to be part
of the package automatically, but apparently it gets easily confused,
so this change explicitly sets it.

This fixes #81.

pyproject.toml

@@ -39,5 +39,8 @@ line-length = 79
 [tool.ruff.format]
 quote-style = "single"
 
+[tool.setuptools]
+packages = [ "json5" ]
+
 [tool.setuptools.dynamic]
 version = {attr = "json5.__version__"}