Update GitHub workflow publish_release

[ClaasRostock]

• .github/workflows/publish_release.yml : Run publishing job from main (non-reusable) workflow.
• Remove the two reusable workflows _publish_package.yml and _publish_package_test.yml.
• Update the trusted publishing settings on pypi to 'publish_release.yml' as the workflow name running the publishing step.

Background for this change is a limitation recently introduced on pypi, which does not allow anylonger to run the GitHub action 'pypa/gh-action-pypi-publish' from a reusable workflow. The code hence needed to be moved upwards, from the reusable workflow _publish_package.yml into the (non-reusable) workflow publish_release.yml
See https://github.com/marketplace/actions/pypi-publish -> Note under "Trusted Publishing"