ci: Bugfix for per-commit CI

Since github will take the definition of the workflow from the merge
commit, we need to take the .ci scripts from there as well. If we check
out the .ci scripts from the current commit it might not match the
workflow definition.

Author: NickeZ

.github/workflows/pr-ci.yml

@@ -58,10 +58,12 @@ jobs:
           GIT_COMMITTER_NAME: Bot
           GIT_COMMITTER_EMAIL: bot@bitbox.swiss
         run: |
-          git fetch origin ${{ matrix.commit }}
+          git fetch origin ${{ matrix.commit }} ${{ github.event.pull_request.merge_commit_sha }}
           git merge --no-ff --no-edit ${{ matrix.commit }}
-          echo "merge commit parents:"
           git log -1 --format="Head %H, Parents %P"
+          # Since the workflow definition is taken from the pull request merge commit, we need to
+          # get the .ci scripts from there as well.
+          git checkout -f ${{ github.event.pull_request.merge_commit_sha }} -- .ci .github
 
       - name: Pull container image
         run: ./.ci/run-container-ci pull