Don't check .gitignore files in parent directories

When building inside a .gitignore'd output directory as part of
another build system maturin may accidentially pick up the parent
.gitignore. Lets just disable searching for parent .gitignore
files since this functionality is broken anyways as the logic does
not match git's .gitignore logic anyways.

For example in buildroot we have an output directory that has its
contents gitignored in which maturin will build packages, changing
some minor implementation details in how we ignore this directory
triggered this bug.

buildroot/buildroot@a14c862

As the output dir files are supposed to be ignored both before and
after this change this indicates that ignore::WalkBuilder parent
matching is fundamentally broken and can not be used reliably
in the first place as it does not match git's ignore logic.

Signed-off-by: James Hilliard <[email protected]>

src/module_writer.rs

@@ -1286,7 +1286,11 @@ pub fn write_python_part(
     }
 
     for package in python_packages {
-        for absolute in WalkBuilder::new(package).hidden(false).build() {
+        for absolute in WalkBuilder::new(package)
+        .hidden(false)
+        .parents(false)
+        .build()
+        {
             let absolute = absolute?.into_path();
             let relative = absolute.strip_prefix(python_dir).unwrap();
             if absolute.is_dir() {