v2.4.0 - support local execution with act

[dorny]

• Removed restriction to mark all as added when push.ref or base input refers to tag
• Use git log to detect changes from PRs merge commit when Github auth token is not available
• Improved processing of repository initial push:
  • all files are marked as added
• Improved processing of first push of new branch
  • if SHA of previous push is not available it will fallback to detect changes against merge-base with default branch
• Support local execution with act
  • Fallback behavior for missing event payload data
  • No requests to remote if all needed is already available locally - act images doesn't have proper git/ssh configuration against github so it would fail otherwise

Closes #39
Closes #33