Support nested `.gitignore`

[fabalchemy]

Bug

When a subdirectory has an "unignore" directive in its .gitignore, Spell Checker still excludes the matching files, indicating that they are ignored because of the root .gitignore.

Steps to reproduce

git init repro
cd repro
echo '*.md' > .gitignore
mkdir a && cd a
echo '!*.md' > .gitignore
touch test.md
code .