Trim message when exceeds maximum characters

[ljetten]

Partially solving #93 to at least not have the github action fail when message from path exceeds maximum characters set by GitHub.

Used kishaningithub/github-actions-expermiments#1 (comment) message to test.

[glureau]

Thanks for your work! Note that this won't be able to properly cut the markdown syntax. (Thanksfully github should be able to handle that in most cases.)