act interprets Branch names (the @master portion in uses = "/abc/def@master") as case insensitive, which differs from GitHub.

This results in different behavior between local and GitHub environment.

Any Repository/Action should be fine for testing, but for the sake of completeness:

• Create an action as described in this README.md
• run the action -> success
• change the case in uses = "jakobgalbavy/github-actions/slack-message@master" to @Master and run the action -> succeeds locally, fails on GitHub