"format_output: false" runs prettier

[evanwill]

I have been using jekyll-action-ts and just ran into an issue where build was interrupted by an error from prettier. I didn't realize I was using prettier, because I thought I had turned if off using the option format_output: false.

After poking around the action, I realized that prettier is off by default, but if you add any value to format_output it is on. From my quick reading I had mistakenly thought that prettier was on by default, and that I had to turn it off, thus the format_output: false.

It would be helpful to clarify that point in the README, and/or update the action to check for specifically for format_output: true (rather than just any value).

Thank you for this action!