workflows: Remove overwrite of base-branch variable

No need for overwrite defaults to origin/main which is for now the main use
case. Still variable could be used if needed.

Author: umaucher

.github/workflows/gitlint.yml

@@ -29,4 +29,3 @@ jobs:
         uses: ./.github/actions/gitlint
         with:
           pr-number: ${{ github.event.number }}
-          base-branch: ${{ github.event.pull_request.base.ref }}