ci: Merge master in test-each-commit task (take 2)

* Run git config earlier and only once
* Run git merge in the yaml, before calling the bash script
* Run git reset in the yaml as well, for symmetry
* Replace "git merge --abort" with "git reset --hard", because it does
  not fail when already up to date and no merge was started.

.github/workflows/ci.yml

@@ -73,13 +73,15 @@ jobs:
           echo "TEST_BASE=$(git rev-list -n$((${{ env.MAX_COUNT }} + 1)) --reverse HEAD $EXCLUDE_MERGE_BASE_ANCESTORS | head -1)" >> "$GITHUB_ENV"
       - run: |
           git fetch origin master
+          git config user.email "ci@example.com"
+          git config user.name "CI"
       - run: |
           sudo apt-get update
           sudo apt-get install clang ccache build-essential cmake ninja-build pkgconf python3-zmq libevent-dev libboost-dev libsqlite3-dev libdb++-dev systemtap-sdt-dev libzmq3-dev qt6-base-dev qt6-tools-dev qt6-l10n-tools libqrencode-dev -y
       - name: Compile and run tests
         run: |
           # Run tests on commits after the last merge commit and before the PR head commit
-          git rebase --exec "./.github/ci-test-each-commit-exec.sh" ${{ env.TEST_BASE }}
+          git rebase --exec "git merge --no-commit origin/master && ./.github/ci-test-each-commit-exec.sh && git reset --hard" ${{ env.TEST_BASE }}
 
   macos-native-arm64:
     name: ${{ matrix.job-name }}