Avoid duplicate CI runs for pull requests made from the same repo. (#485

)

.github/workflows/ci.yml

@@ -9,6 +9,11 @@ env:
 
 jobs:
   check-style:
+    # Do not run this job for pull requests where both branches are from the same repo.
+    # Jobs that depend on this one will be skipped too.
+    # This prevents duplicate CI runs for our own pull requests, whilst preserving the ability to
+    # run the CI for each branch push to a fork, and for each pull request originating from a fork.
+    if: github.event_name == 'push' || github.event.pull_request.head.repo.id != github.event.pull_request.base.repo.id
     runs-on: windows-latest
     steps:
       - name: Checkout
@@ -54,6 +59,11 @@ jobs:
 
   # Setup the OS matrix so that CUDA tests do not run on forks, as it needs self-hosted runners
   setup-os-matrix:
+    # Do not run this job for pull requests where both branches are from the same repo.
+    # Jobs that depend on this one will be skipped too.
+    # This prevents duplicate CI runs for our own pull requests, whilst preserving the ability to
+    # run the CI for each branch push to a fork, and for each pull request originating from a fork.
+    if: github.event_name == 'push' || github.event.pull_request.head.repo.id != github.event.pull_request.base.repo.id
     runs-on: ubuntu-latest
     steps:
       - name: Setup OS matrix
@@ -67,7 +77,6 @@ jobs:
       os: ${{ steps.setup-os-matrix.outputs.os }}
 
   build-and-test:
-    if: github.event_name == 'push' || github.event.pull_request.head.repo.id != github.event.pull_request.base.repo.id
     needs: setup-os-matrix
     strategy:
       matrix: