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##### SUMMARY
The "source" folder of my collection contains several files that are not directly related to the collection itself. E.g. a `.gitignore`, a `.github` folder, a `Makefile` etc.
When using `ansible-galaxy collection build <folder>`, these files are included in the generated tarball. This is especially hurtful when the source folder also contains a Python venv that I use for developing.

##### ISSUE TYPE
- Bug Report

##### COMPONENT NAME
ansible-galaxy

##### ANSIBLE VERSION
<!--- Paste verbatim output from "ansible --version" between quotes -->
```paste below
ansible 2.9.0.dev0
  config file = /etc/ansible/ansible.cfg
  configured module search path = [u'/home/egolov/.ansible/plugins/modules', u'/usr/share/ansible/plugins/modules']
  ansible python module location = /home/egolov/Devel/ansible/ansible/lib/ansible
  executable location = /home/egolov/Devel/ansible/ansible/bin/ansible
  python version = 2.7.15 (default, Oct 15 2018, 15:26:09) [GCC 8.2.1 20180801 (Red Hat 8.2.1-2)]

```

##### CONFIGURATION
<!--- Paste verbatim output from "ansible-config dump --only-changed" between quotes -->
```paste below
empty
```

##### OS / ENVIRONMENT
Fedora


##### STEPS TO REPRODUCE
Build a collection :)

##### EXPECTED RESULTS
I'd expect only collection-relevant files/folders (those that are listed in the spec/docs) to be included.


##### ADDITIONAL INFORMATION
Alternatively, a ignore file as suggested by @bcoca  in https://github.com/ansible/ansible/pull/59121/files#r304554334 could be a fix for this.

temp_dir = to_bytes(tmp_path_factory.mktemp('test-ÅÑŚÌβŁÈ Collections'))
    data = b"\x00\x01\x02\x03"
    sha256_hash = sha256()
    sha256_hash.update(data)
    mock_open = MagicMock()
    mock_open.return_value = BytesIO(data)
    monkeypatch.setattr(collection, 'open_url', mock_open)
    expected = os.path.join(temp_dir, b'file')
    actual = collection._download_file('http://google.com/file', temp_dir, sha256_hash.hexdigest(), True)
    assert actual.startswith(expected)
    assert os.path.isfile(actual)
    with open(actual, 'rb') as file_obj:
        assert file_obj.read() == data
    assert mock_open.call_count == 1
    assert mock_open.mock_calls[0][1][0] == 'http://google.com/file'
def test_download_file_hash_mismatch(tmp_path_factory, monkeypatch):