ci: fix version bump workflow and make sure in future we get notified

[derberg]

related to https://github.com/asyncapi/dotnet-nats-template/actions/runs/2536516647 and we learned that for at least a month the version bump workflow doesn't work

this PR:

• make sure bump version works the same way release and pr testing workflows
• add slack notifications in case of these workflows fail

[derberg]

@fmvilas this one is pretty critical senior 😄

[derberg]

/rtm