Trigger automatic rebase on issue comment (#1695)

* Trigger automatic rebase on issue comment

Instead of `pull_request` event (created, closed, etc.).

Fixes https://github.com/cirrus-actions/rebase/issues/43

* Removed workaround

.github/workflows/rebase.yml

@@ -1,8 +1,9 @@
 name: Automatic Rebase
 # https://github.com/marketplace/actions/automatic-rebase
 
-on:
-  - pull_request
+on: 
+  issue_comment:
+    types: [created]
 
 jobs:
   rebase:
@@ -17,10 +18,3 @@ jobs:
       uses: cirrus-actions/rebase@1.2
       env:
         GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-  # https://github.community/t5/GitHub-Actions/Workflow-is-failing-if-no-job-can-be-ran-due-to-condition/m-p/38186#M3250
-  always_job:
-    name: Always run job
-    runs-on: ubuntu-latest
-    steps:
-      - name: Always run
-        run: echo "This job is used to prevent the workflow to fail when all other jobs are skipped."