build: Specify package (CI autodiscovers "node_modules" otherwise)

pyproject.toml

@@ -2,6 +2,7 @@
 requires = ["setuptools>=61.2"]
 build-backend = "setuptools.build_meta"
 
+# This project is not intended to be released or used as a Python package. This file only exists for babel.
 [project]
 name = "ocdsextensionexplorer"
 version = "0.0.0"
@@ -10,6 +11,9 @@ license = {text = "BSD"}
 [project.entry-points."babel.extractors"]
 tag = "extension_explorer.extract:extract_tag"
 
+[tool.setuptools]
+packages = ["extension_explorer"]
+
 [tool.isort]
 profile = "black"
 line_length = 119