The action fails if the main branch already exists

Nobody has claimed this yet.

I believe there is an issue on **entrypoint.sh**. I used this action to merge a pull request that was previously auto approved. In my GitHub repository, my principal branch is main and there is a command in the entrypoint.sh in line 41.

git checkout -b "${HEAD_BRANCH}" origin/"${HEAD_BRANCH}"

This produces this error:
fatal: a branch named 'main' already exists

This could be overcome with the following code:

if git branch --list | grep -q "${HEAD_BRANCH}"; then
echo "Branch ${HEAD_BRANCH} already exists, checking it out."
git checkout "${HEAD_BRANCH}"
else
echo "Creating a new branch ${HEAD_BRANCH}."
git checkout -b "${HEAD_BRANCH}" origin/"${HEAD_BRANCH}"
fi

The indentation of the above snipped is not working while writing the issue.

Start with entrypoint.sh around line 41 and reproduce the action with a repository whose principal branch is already named main. Check the branch-selection behavior when ${HEAD_BRANCH} already exists, then verify the action can continue its pull-request merge without the fatal branch-name error.

Written by the indexing model from the issue text.