When I released PHPUnit versions 8.5.44, 9.6.25, 10.5.53, 11.5.34 and 12.3.6, GitHub Actions did not run the release workflow (https://github.com/sebastianbergmann/phpunit/blob/12.3.6/.github/workflows/release.yaml, for example). Therefore, these versions only have Git tags (which Packagist uses, of course), but no releases were created on GitHub.

As far as I know, this is the first time this has happened.

I asked for help on phpc.social. According to @ghostwriter (https://phpc.social/deck/@ghostwriter/115066710988910605), on.push.tags fires once per Git push, not per tag. However, pushing multiple tags at the same time (git push --tags) was not a problem and the release workflow was run for each tag.