ignore: negation with single * wildcard is not applied to directory paths

[pmrowla]

Related: iterative/dvc#6995

Given this directory structure:

$ tree .
.
└── data
    ├── test
    └── test.dvc

2 directories, 2 files

And this gitignore:

$ cat .gitignore
data/**
!data/*/
!*.dvc

CLI Git only ignores data/test.dvc, but dulwich treats data/ as ignored:

$ git check-ignore data/ data/test.dvc data/test
data/test
$ python -m dulwich check-ignore data/ data/test.dvc data/test
data/
data/test

If you change negation pattern to use a ** wildcard dulwich works as expected:

$ cat .gitignore
data/**
!data/**/
!*.dvc
$ git check-ignore data/ data/test.dvc data/test
data/test
$ python -m dulwich check-ignore data/ data/test.dvc data/test
data/test