Fix the merge workflow

.github/workflows/merge-upstream.yml

@@ -6,13 +6,15 @@ on:
     - cron: '0 8 * * 5'
 
 jobs:
-  job:
+  create-pr:
     runs-on: ubuntu-latest
 
     steps:
 
     - uses: actions/checkout@v3
       with:
+        fetch-depth: 0
+        sparse-checkout: '.'
         ref: akirak
 
     - name: Switch to a work branch
@@ -21,21 +23,33 @@ jobs:
     - name: Fetch the upstream
       run: |
         git remote add upstream https://github.com/melpa/melpa.git
-        git fetch upstream
+        git fetch upstream master
 
     - uses: DeterminateSystems/nix-installer-action@v4
       with:
         diagnostic-endpoint: ''
 
     - name: Merge upstream recipes
       run: |
-        nix run github:emacs-twist/recipes-updater --no-write-lock-file \
-            -- upstream/master
+        # Set some identity. Actually it will be overridden later, so it's
+        # unused
+        git config --add user.name 'github-actions[bot]'
+        git config --add user.email '6270544+github-actions[bot]@users.noreply.github.com'
+        nix run github:emacs-twist/recipes-updater/remain-on-tmp-branch#forceUpdate \
+          --no-write-lock-file -- upstream/master
+        git rebase akirak
+
+    # A workaround to prevent peter-evans/create-pull-request from resetting the
+    # head here:
+    # <https://github.com/peter-evans/create-pull-request/blob/d806186ee3288c60a352af9852b6b18afbbfd87e/src/create-or-update-branch.ts#L178>
+    - name: Detach the head
+      run: git switch --detach `git rev-parse HEAD`
 
     - name: Create a pull request
       uses: peter-evans/create-pull-request@v5
       with:
         base: akirak
         token: ${{ secrets.PAT_FOR_PR }}
         title: 'Merge the upstream recipe commits'
+        branch: create-pull-request/merge-recipes
         labels: automation