ci: test packaging on PRs, too

Author: offbyone

.github/workflows/release.yml

@@ -31,7 +31,6 @@ jobs:
 
       - uses: hynek/build-and-inspect-python-package@v2
 
-  # Upload to Test PyPI on every commit on main.
   publish-test-release:
     permissions:
       contents: read
@@ -40,7 +39,9 @@ jobs:
 
     name: Publish in-dev package to test.pypi.org
     environment: publish-test-release
-    if: github.event_name == 'push' && github.ref == 'refs/heads/main'
+    if: |
+      (github.event_name == 'push' && github.ref == 'refs/heads/main') ||
+      (github.event_name == 'pull_request')
     runs-on: ubuntu-latest
     needs:
       - pure-python-wheel-and-sdist