Proposal for Pull Request fetch method

It appears the existing branch fetch method has implementation limitations when using GitHub's Fork & Pull strategy.

Currently, the process attempts to fetch the forked branch from origin. As a result, if a PR is created from a branch that exists only on the fork (and not on origin), an error occurs because the ref cannot be found in origin.

How about we change the fetch method to use the hidden ref, to improve this so it works well with the Fork & Pull strategy?

The example is as follows:
https://github.com/kuckjwi0928/claude-code-action/commit/7a6b6a0514316a03ff643f9355e696cdb76d6200

If my understanding is incorrect, I would appreciate it if you could provide a setup guide for the Fork & Pull strategy.