CI: run tests on all branch pushes, once per same-repo PR

The previous condition (github.event.pull_request == null) did not work:
github.event.pull_request is always null on push events regardless of whether
a PR exists, so the redundant run was never skipped.

Correct condition keeps on: [push, pull_request] and runs tests on every
branch push while avoiding the duplicate when a same-repo PR exists:

- push event: always runs (push to any branch, PR or not). On a push event
  github.event.pull_request.head.repo.fork dereferences to an empty string
  (falsy, no error), so the negation is true.
- same-repo PR: skipped, since that push already triggered a run.
- fork PR: runs via pull_request, since forks can't trigger a push here.

Verified against GitHub docs: dereferencing a missing context property
yields an empty string rather than an error.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

Author: const-cloudinary

.github/workflows/test.yml

@@ -4,8 +4,12 @@ on: [push, pull_request]
 
 jobs:
   build:
-    # Skip redundant runs: don't run on push if there's an associated PR
-    if: github.event_name == 'pull_request' || github.event.pull_request == null
+    # Run on every branch push, but avoid duplicate runs when a same-repo PR
+    # exists: same-repo changes run via the push event, while fork PRs (which
+    # can't trigger a push in this repo) run via the pull_request event.
+    if: >-
+      (github.event_name == 'push' && !github.event.pull_request.head.repo.fork) ||
+      (github.event_name == 'pull_request' && github.event.pull_request.head.repo.fork)
     runs-on: ubuntu-24.04  # noble equivalent
 
     strategy: