zoekt: update to ignore non-fatal ctag errors
Created by: keegancsmith
We recently introduced hard failures when encountering a ctags error. However, there are a small number of repos (2 at the moment) which output a non-fatal error that we can ignore. For example:
ignoring null tag in keybinding-emacs.js(line: 831)
https://github.com/sourcegraph/zoekt/compare/a99799fdc041...dae6fc7ecc8f