Adding tags to Soundcloud files raises TypeError

[declension]

Steps to replicate

• SoundCloud file
• Edit tags
• Click add

https://sentry.io/organizations/quodlibet/issues/3496751361/?referrer=github_plugin

TypeError: Expected string but got 0.4980392156862745<class 'float'>
(3 additional frame(s) were not displayed)
...
  File "gi/overrides/Gtk.py", line 1007, in _do_insert
    row, columns = self._convert_row(row)
  File "gi/overrides/Gtk.py", line 907, in _convert_row
    result.append(self._convert_value(cur_col, value))
  File "gi/overrides/Gtk.py", line 921, in _convert_value
    return GObject.Value(self.get_column_type(column), value)
  File "gi/overrides/GObject.py", line 208, in __init__
    self.set_value(py_value)
  File "gi/overrides/GObject.py", line 240, in set_value
    raise TypeError("Expected string but got %s%s" %

TypeError: Expected string but got 0.4980392156862745<class 'float'>