fix(ci): match dependabot PR author instead of github.actor

github.actor devient le login de la personne qui relance le workflow lors
d'un re-run manuel, ce qui saute silencieusement le job d'auto-merge.
github.event.pull_request.user.login décrit l'auteur de la PR et ne varie
pas au re-run.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: rlespinasse

.github/workflows/dependabot-auto-merge.yml

@@ -8,7 +8,7 @@ permissions:
 
 jobs:
   auto-merge:
-    if: github.actor == 'dependabot[bot]'
+    if: github.event.pull_request.user.login == 'dependabot[bot]'
     runs-on: ubuntu-latest
     steps:
       - name: Dependabot metadata