Issues are not propagated to github due to newlines

[Limess]

When testing this service we discovered a bug on Github where issues with newlines in titles do not get propagated to Slack when using the official Github Slack application (i.e. /github subscribe <org>/<repo> issues).

We've raised this with Github support, but this should be fixed in the library to prevent confusion - this is a result of the template creating a trailing newline in the issue, for example we were seeing this title in the request when using the default template:

"title":"[ALERT] alertname:TicketAlertTestV6 monitor:prometheus repo:data-platform-documentation severity:ticket system:system-monitoring \n"