`setuptools_scm` includes a committed `.gitignore` to an `sdist` package

Question

I have a flat-layout project like this:

├── project_name
│   └── ...
├── .gitignore
├── pyproject.toml
└── ...

I follow the setuptools docs to compose the pyproject.toml like this:

[build-system]
requires = ['setuptools>=45', 'setuptools_scm[toml]>=6.2']

[project]
name = 'project_name'
version = '0.0.1'

[tool.setuptools.exclude-package-data]
"*" = [".gitignore"]

However, when I do

python3 -m build --sdist

I get the .gitignore file in the resulting *.tar.gz file.

I can forcefully exclude the file using a MANIFEST.in:

exclude .gitignore

What the use of the [tool.setuptools.exclude-package-data] section, then? Can I do the job without the MANIFEST.in file?

Do I misuse the section? From what the building process reports, I guess the '*' there means the project_name directory. Is there any config key to exclude the .* files from the root of the sdist package?

---

An MWE for @sinoroc (to be run in a shell):

# make a dedicated directory and enter it
mkdir package_name
pushd package_name

# make two empty files (only the first one is mandatory)
touch .gitignore README

# fill pyproject.toml
echo "build-system.requires = ['setuptools', 'setuptools_scm[toml]']" >> pyproject.toml
echo "project = {name = 'package_name', version = '0.0.1'}"           >> pyproject.toml
echo "[tool.setuptools_scm]"                                          >> pyproject.toml

# prepare a virtual environment
python -m venv venv
source venv/bin/activate
python -m pip install -U pip setuptools build

# commit .gitignore
git init
git add -f .gitignore
git commit -m "add .gitignore"

# build a package
python -m build --sdist

# list the files in the package
tar --list -f dist/package_name-0.0.1.tar.gz

# exit (optional)
deactivate
popd

This makes the following file tree:

├── .git
│   └── ...
├── dist
│   └── package_name-0.0.1.tar.gz
├── package_name.egg-info
│   └── ...
├── venv
│   └── ...
├── .gitignore
├── pyproject.toml
└── README

The pyproject.toml file has the following content:

build-system.requires = ['setuptools', 'setuptools_scm[toml]']
project = {name = 'package_name', version = '0.0.1'}
[tool.setuptools_scm]

The README and .gitignore files are empty. The latter has to be committed for the MWE to work.

It looks that it's the setuptools_scm that's to blame for the inclusion of .gitignore. The latter should be committed.