UTF-8, invalid characters as a result of AlternativeText

[joca2]

Hello
when I use UTF-8 and

$ message = (new FormattedMessageFactory())
                 ->withHtml(<p>zażółć gęślą jaźń</p>) ...

I have invalid characters in alternative text.
The problem is probably in AlternativeText::fromHtml($html) which uses: DOMDocument->loadHTML() which recodes characters.
regards

[frederikbosch]

I added a test for it, but it does not lead to any bugs, see the test where this HTML is correctly transformed into this alternative text.