Backport-action 0.0.6

Features

• add placeholder ${pull_author} for username of the original pull request's author #84

Bug fixes

• pull request cannot be backported when branch is deleted from github #90

Other

• deprecate version input #103
  From now on, users no longer need to provide this input. Previously, this input was required by the action and had to be kept in-sync with the action's version. For backwards compatibility it was deprecated, but it is no longer used for anything. Users can safely remove it from the with section of their workflow.
• fetch all necessary git refs #162
  The backport action now fetches only the necessary git history. Previously, users had to set fetch-depth: 0 for the actions/checkout@v2 action, to fetch the entire git history. This is no longer needed.
• update dependencies to latest available