files with multiple dots in the file name not matched

I'm told I have a validation error:

```
$ github-codeowners validate
Found rules which did not match any files [
  '/test.en.yml @org/team',
]
```

But in reality the file exists:

```
$ ls test.en.yml
test.en.yml
```

Had a browse around the codebase and didn't spot the bug, sorry.