ci: do not run cd when a branch is created

[radu-mocanu]

CD triggers on pushes to main and release/** filtered to pyproject.toml. Creating a release/* branch at a commit that touched pyproject.toml is a push that can match that filter, so the branch creation itself starts a publish run for a version that was already released.

Today PyPI rejects the duplicate upload, so the run just goes red. It is not harmless in every case: if the base commit's version bump was never actually published, branch creation would publish it from a branch nobody treated as a release.

Gate the CD entry jobs on !github.event.created. build needs lint and test, and pypi-publish needs build, so skipping the two entry jobs skips the chain. Manual workflow_dispatch runs are unaffected, since the property is absent there and evaluates as falsy.

Merging a hotfix PR into a release branch is a normal push with commits, so created is false and the publish still runs as intended.