[llvm] [Github] Force files changed step in docs action to use GH API (PR #69763)

[Aiden Grossman via llvm-commits]

boomanaiden154 wrote:

Yes. If there isn't a checkout, it uses the Github API. A comment is a good point. I'll add one in.

I'm planning on doing this for the code formatting action too but wanted to do it in a separate PR as I don't understand all the details of that action and want Tobias to make sure my changes won't disturb anything and I assume he's out for the weekend at this point.

https://github.com/llvm/llvm-project/pull/69763