Update to peter-evans/create-pull-request to v8

* Same as https://github.com/ruby/setup-ruby/blob/master/.github/workflows/check-new-windows-versions.yml

Author: eregon

.github/actions/create-pr-to-setup-ruby/action.yml

@@ -25,7 +25,7 @@ runs:
     - run: ./pre-commit
       shell: bash
 
-    - uses: peter-evans/create-pull-request@v3
+    - uses: peter-evans/create-pull-request@v8
       id: pr
       with:
         push-to-fork: ruby-builder-bot/setup-ruby