lts-watch-* labels should not be applied when dont-land-on-* exist
As the title says, if for example a PR has the 'dont-land-on-v6.x' label already, then the bot should not try to add an 'lts-watch-v6.x' label.
@mscdex do you have an example of this happening? I think in most cases it will not land cleanly then.
@Fishrock123 Example: https://github.com/nodejs/node/pull/10445
node v6.x and older do not have a fast function.bind(), so that PR should not be backported.
Bump, happened in https://github.com/nodejs/node/pull/10839#event-931668098

@gibfahn It might be a good idea to merge these discussions on backport-related issues into the newly created issue here: https://github.com/nodejs/github-bot/issues/120 so that we can compile a list of issues.