Remove refs/heads from incoming branch variable

[aka-tpayne]

I ran into an issue where the branch variable was coming in with refs/heads.

- name: Create Branch
    uses: peterjgrainger/action-create-branch@master
    env:
        GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
    with:
        branch: ${{ github.ref }}-deploy

[peterjgrainger]

@aka-tpayne thanks for the contribution:)