Ignore (for now) text-attributes-changed signals from LibreOffice

LibreOffice emits this signal nearly every time text is typed,
even though the text attributes haven't changed:
https://bugs.freedesktop.org/show_bug.cgi?id=71556

LibreOffice fails to emit this signal the main time we are looking
for it, namely to present that a misspelled word was typed:
https://bugs.freedesktop.org/show_bug.cgi?id=71558

Useless signals are useless.