Apply ruff/pycodestyle rule E721 (#347)

E721 Do not compare types, use `isinstance()`

xmltodict.py

@@ -443,7 +443,7 @@ def _emit(key, value, content_handler,
                 attrs[ik[len(attr_prefix):]] = iv
                 continue
             children.append((ik, iv))
-        if type(indent) is int:
+        if isinstance(indent, int):
             indent = ' ' * indent
         if pretty:
             content_handler.ignorableWhitespace(depth * indent)