Ensure HTML is read as UTF-8

This has been tested on Windows where Python could
detect HTML files as a windows codepage
rather than UTF-8.

As it seems Sphinx generates HTML in UTF-8, it should
be safe to enforce it here.

doxysphinx/html_parser.py

@@ -484,7 +484,7 @@ def parse(self, file: Path) -> HtmlParseResult:
         :return: The result of the parsing
         :rtype: ParseResult
         """
-        buffer = file.read_text()
+        buffer = file.read_text(encoding="utf-8")
         tree = etree.document_fromstring(buffer).getroottree()
 
         meta_title, project, title = self._read_project_and_title(buffer, file)