Bug - the text `[:tag]` shows up notifications after 8.3.0

[uberbrady]

A user reports:

I upgraded to v8.3.0 this morning, since then we've noticed that the addition of Asset tags to subject line at check in/out results in a stray [:tag] in our Mattermost notifications. I've tried using both the Slack and Webhook integrations, the behaviour is present in both.

Apparently, works fine in emails.

[snipe]

@uberbrady @Godmartinz has a WIP to fix this btw