Add unlocked workflow step to releasing documentation

Author: sim642

docs/developer-guide/releasing.md

@@ -16,18 +16,22 @@
 
     All changes must be committed because the working tree is not checked.
 
-6. Update `CHANGELOG.md`:
+6. Check that "unlocked" workflow passes on GitHub Actions.
+
+    It can be run manually on the release branch for checking.
+
+7. Update `CHANGELOG.md`:
 
     1. Add a desired version number (`vX.Y.Z`) header at the top.
     2. Add a list of biggest changes compared to the previous version.
 
-7. Update list of authors in `CITATION.cff` and `dune-project`.
-8. Tag the release: `dune-release tag`.
-9. Create the distribution archive: `dune-release distrib`.
-10. Create a GitHub release with the git tag: `DUNE_RELEASE_DELEGATE=github-dune-release-delegate dune-release publish distrib`.
+8. Update list of authors in `CITATION.cff` and `dune-project`.
+9. Tag the release: `dune-release tag`.
+10. Create the distribution archive: `dune-release distrib`.
+11. Create a GitHub release with the git tag: `DUNE_RELEASE_DELEGATE=github-dune-release-delegate dune-release publish distrib`.
 
     Explicitly specify `distrib` because we don't want to publish OCaml API docs.
     Environment variable workaround for the package having a Read the Docs `doc` URL (see <https://github.com/ocamllabs/dune-release/issues/154>).
 
-11. Create an opam package: `dune-release opam pkg`.
-12. Submit the opam package to opam-repository: `dune-release opam submit`.
+12. Create an opam package: `dune-release opam pkg`.
+13. Submit the opam package to opam-repository: `dune-release opam submit`.