Exclude test data

Fixes #5925 in a minimally invasive way.

onnx/backend/test/data contains large test files which should not be
included in the PyPI package. This PR simply excludes them when
building the package. This reduces the size of the `onnx`
package (uncompressed) from 51MB to 12MB.

Signed-off-by: Christian Bourjau <christian.bourjau@quantco.com>

pyproject.toml

@@ -47,6 +47,11 @@ onnx = [
     "py.typed",
 ]
 
+[tool.setuptools.exclude-package-data]
+onnx = [
+     "backend/test/data/**/*",
+]
+
 [tool.pytest.ini_options]
 
 addopts = "--nbval --nbval-current-env --tb=short --color=yes"