--ignore /math works, but --ignore /math/arm does not

### Description

If I use `--ignore /math` then the whole math folder is ignored.
If I use `--ignore /math/arm` instead, I would now expect that the subfolder arm in the folder math is ignored. Instead, the folder is not ignored at all.
I also tried `--ignore /math/arm/*`, but it didn't work either.

I also tried removing the leading `/`, but that didn't improve things.

### How To Reproduce

Pass the above `--ignore` options.

### System configuration

* OS: Arch Linux
* Python verson 3.11.3
* scancode version 31.2.6
* installation method: pip install --user scancode-toolkit