.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.

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"

.github/workflows/publish_release.yml

@@ -10,9 +10,21 @@ jobs:
   build_package:
     uses: ./.github/workflows/_build_package.yml
   publish_package:
+    name: Publish package
     needs:
       - build_package
-    uses: ./.github/workflows/_publish_package.yml
+    runs-on: ubuntu-latest
+    environment: release
+    permissions:
+      id-token: write
+    steps:
+      - uses: actions/download-artifact@v4
+        with:
+          name: artifact
+          path: dist
+      - uses: pypa/gh-action-pypi-publish@release/v1
+        # with:                                             # Uncomment this line to publish to testpypi
+        #   repository-url: https://test.pypi.org/legacy/   # Uncomment this line to publish to testpypi
   merge_into_release:
     uses: ./.github/workflows/_merge_into_release.yml
     secrets: