[merge-release-in-main.yml] Replace action repo-sync/pull-request with gh cli

[mikeharder]

typespec/.github/workflows/merge-release-in-main.yml

Lines 36 to 38 in c1cc310

	- name: create pull request
	id: open-pr
	uses: repo-sync/pull-request@v2

The action on L38 is deprecated, and I think can be replace with the GH CLI.