revert(workflow): auto-assign PR author (#1392)

Motivation
----------
 #1388 was the third PR that ran into a complexity of
 `pull_request_target`: Since the `root.yml` workflow would run on the
 base branch where the changes to `auto-assign` was not present, the
 new workflow was not tested.

How to test
-----------
1. We need admin powers to merge this, as it will turn red
2. After merge, new PRs should be green again

Co-authored-by: Hannes Heine <heine.hannes@gmail.com>

.github/workflows/pr.yml

@@ -12,13 +12,6 @@ permissions:
   statuses: write
 
 jobs:
-  assign-author:
-    runs-on: ubuntu-latest
-    steps:
-      - uses: kentaro-m/auto-assign-action@v2.0.0
-        with:
-          configuration-path: '.github/auto-assign.yml'
-
   main:
     name: Validate PR title
     runs-on: ubuntu-latest