Don't run this on branches in our own org

We would trigger both on push and pull_request, skip the 2nd one.

So we either run when this is a push in our organisation but not to
main,
OR if this is a pull_request from another organisation/user to
domjudge_org.

Author: Michael Vasseur

.github/workflows/build-contributor-container-PR.yml

@@ -10,7 +10,10 @@ on:
 
 jobs:
   pr-contributor:
-    if: ${{ github.repository != 'domjudge/domjudge-packaging' || github.ref != 'refs/heads/main' }} 
+    if: ${{ !(github.repository == 'domjudge/domjudge-packaging' &&
+              github.ref == 'refs/heads/main') &&
+            (github.event_name == 'pull_request_target' ||
+             github.event.pull_request.head.repo.full_name != github.repository) }}
     runs-on: ubuntu-latest
     steps:
       - name: Checkout

.github/workflows/build-domjudge-container-PR.yml

@@ -11,7 +11,10 @@ env:
 
 jobs:
   pr-domjudge:
-    if: ${{ github.repository != 'domjudge/domjudge-packaging' || github.ref != 'refs/heads/main' }} 
+    if: ${{ !(github.repository == 'domjudge/domjudge-packaging' &&
+              github.ref == 'refs/heads/main') &&
+            (github.event_name == 'pull_request_target' ||
+             github.event.pull_request.head.repo.full_name != github.repository) }}
     runs-on: ubuntu-latest
     steps:
       - name: Checkout

.github/workflows/build-gitlab-container-PR.yml

@@ -8,7 +8,10 @@ on:
 
 jobs:
   pr-gitlab:
-    if: ${{ github.repository != 'domjudge/domjudge-packaging' || github.ref != 'refs/heads/main' }} 
+    if: ${{ !(github.repository == 'domjudge/domjudge-packaging' &&
+              github.ref == 'refs/heads/main') &&
+            (github.event_name == 'pull_request_target' ||
+             github.event.pull_request.head.repo.full_name != github.repository) }}
     name: PR GitLab image
     runs-on: ubuntu-latest
     permissions: