chore: use PEP 440 .dev0 versions on main after releases (#2032)

* chore: use PEP 440 .dev0 versions on main after releases

- Release-trigger workflow now adds a dev bump commit (X.Y.(Z+1).dev0)
  on the release branch after tagging, so main gets the dev version
  when the PR merges. The tag still points at the release commit.
- Set current pyproject.toml to 0.4.4.dev0.
- Replace broken release workflow badge with shields.io release badge.

* Update .github/workflows/release-trigger.yml

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

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Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>