Add support for workflow_dispatch events

[karelbemelmans]

(this Code was written by Copilot using Claude Sonnet 4)

When a workflow_dispatch event is triggered:

• The action no longer throws an "unsupported github event" error
• Instead of comparing commits (which doesn't make sense for manual triggers), it uses the default mode behavior
• This generates a matrix containing all directories that match the provided pattern
• The behavior is the same as when defaults=true is used - it lists all matched directories instead of only changed ones