build: disable assistant_to_the_branch_manager on forks

It currently fails as it is triggered on push, but requires an angular-robot-key that forks don't have.

(cherry picked from commit 095c1f4)

Author: cexbrayat

.github/workflows/assistant-to-the-branch-manager.yml

@@ -12,6 +12,7 @@ permissions:
 jobs:
   assistant_to_the_branch_manager:
     runs-on: ubuntu-latest
+    if: github.event.repository.fork == false
     steps:
       - uses: actions/checkout@93cb6efe18208431cddfb8368fd83d5badbf9bfd # v5.0.1
         with: