chore(release-flow): fix stale doc pointers and remove dead badge step

Three findings from #1503:

- src/datajoint/version.py: header comment listed label_prs.yaml /
  release.yaml / post_release.yaml — none exist; actual workflows are
  draft_release.yaml and post_draft_release_published.yaml.
- RELEASE_MEMO.md: Branch Structure table listed master as 2.1.x;
  bumped to 2.3.x to match current line.
- .github/workflows/post_draft_release_published.yaml: removed the
  'Update README.md badge' step. The seds targeted
  <a id='commit-since-release-link'>/<img id='commit-since-release-img'>
  elements that were removed from README in ff04914 (2026-01-04);
  the step ran empty every release, guarded by the follow-up
  git-diff-empty-commit check.

Leaves finding 1 from #1503 (version.py timing at tag) open —
that one is an architectural choice for the maintainer.

Author: MilagrosMarin

.github/workflows/post_draft_release_published.yaml

@@ -47,18 +47,6 @@ jobs:
           git add src/datajoint/version.py
           git commit -m "Update version.py to $VERSION"
           echo "BRANCH_NAME=$BRANCH_NAME" >> $GITHUB_ENV
-      - name: Update README.md badge
-        run: |
-          # commits since the last release
-          NEW_HREF="https://github.com/datajoint/datajoint-python/compare/${{ github.event.release.tag_name }}...master"
-          NEW_SRC="https://img.shields.io/github/commits-since/datajoint/datajoint-python/${{ github.event.release.tag_name }}?color=red"
-          # Update href in the <a> tag
-          sed -i 's|\(<a id="commit-since-release-link"[^>]*href="\)[^"]*\(".*\)|\1'"$NEW_HREF"'\2|' README.md
-          # Update src in the <img> tag
-          sed -i 's|\(<img id="commit-since-release-img"[^>]*src="\)[^"]*\(".*\)|\1'"$NEW_SRC"'\2|' README.md
-          git add README.md
-          # Only commit if there are changes (handles re-runs gracefully)
-          git diff --cached --quiet README.md || git commit -m "Update README.md badge to ${{ github.event.release.tag_name }}"
       - name: Set up Python ${{matrix.py_ver}}
         uses: actions/setup-python@v5
         with:

RELEASE_MEMO.md

@@ -4,7 +4,7 @@
 
 | Branch | Purpose | Version |
 |--------|---------|---------|
-| `master` | Main development | 2.1.x |
+| `master` | Main development | 2.3.x |
 | `maint/2.0` | Maintenance releases | 2.0.x |
 
 For 2.0.x bugfixes:

src/datajoint/version.py

@@ -1,4 +1,4 @@
 # version bump auto managed by Github Actions:
-# label_prs.yaml(prep), release.yaml(bump), post_release.yaml(edit)
+# draft_release.yaml (draft), post_draft_release_published.yaml (bump + PR)
 # manually set this version will be eventually overwritten by the above actions
 __version__ = "2.3.1"