chore: Fixing PR workflow trigger for forks

Author: wchomik

.github/workflows/git-pr-status-checks.yml

@@ -1,10 +1,15 @@
 name: Git PR Status Checks
 
 on:
-  pull_request: {}
-  
+  pull_request:
+    branches:
+      - main
+  pull_request_target:
+    branches:
+      - main
+
 concurrency:
-  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
+  group: ${{ github.event.pull_request.head.repo.full_name }}-${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
   cancel-in-progress: true
 
 permissions:
@@ -14,7 +19,7 @@ permissions:
   actions: write
   checks: write
   statuses: write
-  
+
 jobs:
   pr-status-check:
     uses: "openmcp-project/blueprint-workflows/.github/workflows/git-pr-status-checks.yml@main"