Possible to set a minimum number of runs to keep?

[owennewburn]

Thanks for creating this action! I was looking for one that could do exactly this. I was wondering if it would be possible to add a parameter that sets a minimum number of workflows to keep? My use-case is I want to always retain the most recent run of one of my workflows. I'd be happy to have a go at adding this and opening a PR if you're happy with that.