update submodule that points to bk/emojis
update submodule that points to bk/emojis

I'm not sure what docs uses this submodule for, however I've just
renamed the emojis default branch from master to main so I thought I'd
take the opportunity to refresh all the downstream users of it.

It's been over a year since docs refreshed the emojis submodule, so
there's a few fun new emojis available to use now.

buildkite/docs,buildkite/docs,buildkite/docs,buildkite/docs