Make .gitkeep icon use VCS icon (#6931)

d1y created

This should be a standard recognized by everyone

```bash
mkdir todo
touch todo/.gitkeep # just placeholder
git add todo
git commit
```

Release Notes:

- Added icon for `.gitkeep` files.

Change summary

assets/icons/file_icons/file_types.json | 1 +
1 file changed, 1 insertion(+)

Detailed changes