Remove step to checkout code for commit signing job - it's unused

We don't use the checked out code, so this is a redundant step in
this job.

Author: SimonBarendse

.github/workflows/pr-check-signed-commits.yml

@@ -9,8 +9,5 @@ jobs:
       pull-requests: write
     runs-on: ubuntu-latest
     steps:
-      - name: Check out code
-        uses: actions/checkout@v3
-
       - name: Check signed commits in PR
         uses: 1Password/check-signed-commits-action@main