springboot Polish Slack notification for a build failure that did not generate a build scan

It looks like this at the moment:

spring-boot-2.3.x jdk14-build failed! [build log] [<(build scan not generated)|build scan>]

It should look something like this:

spring-boot-2.3.x jdk14-build failed! [build log] [build scan not generated]

Comment From: wilkinsona

Closing in favour of PR #21673.