Invalid link: '<a href="#...">...</a>'. The file index.md doesn't contain a bookmark named '...'

**Operation System**: `Windows`

**DocFX Version Used**: 2.46

**Template used**: `default`

**Steps to Reproduce**:

1. download extract [attached example](https://github.com/dotnet/docfx/files/3772235/docfx_project.zip)
2. run `docfx.exe docfx.json`

**Expected Behavior**:

Build succeeds without warnings

**Actual Behavior**:

Build succeeds with one warning: Invalid link: `'Link to anchor'. The file index.md doesn't contain a bookmark named 'anchor-with-umlaut-%C3%A4'`

DocFx seems to url-encode special characters (e.g. german Umlaute) in links but does not url encode the anchor names that are being generated for each heading, therefore the warning I guess. Firefox seems to be okay with that (it can navigate the links) but of course it is not obvious anymore whether ones link is really invalid or whether it just contains characters that got url encoded.