Fix gem releases by separating build and publish jobs

[ogajduse]

Tag releases fail because gem build requires man/hammer.1.gz, which is generated and not tracked. Build the man page and gem in a read-only job, then transfer the gem to a separate job with RubyGems OIDC publishing permission. Check that the built gem's versioned filename matches the tag before uploading it.

Related upstream issue: voxpupuli/ruby-release#13

This follows the split-workflow approach discussed in voxpupuli/ruby-release#13 (comment) and needs no upstream action change. The workflow filename and release environment are unchanged. Documentation tooling is installed without recommendations to avoid unnecessary TeX dependencies; no application bundle is installed.

Validation:

• actionlint 1.7.12 (including shellcheck) and git diff --check pass.
• Clean Ubuntu 24.04 container builds succeeded for master, 5.0.1, and 3.19.1 using the direct build recipe. All gems contain the man page and 15 compiled locale files.
• Correct version checks pass; mismatched tag/version checks fail.
• Live GitHub artifact transfer and RubyGems OIDC/publication were not exercised. Container checks used Ubuntu Ruby 3.2.3; the workflow uses ruby/setup-ruby's latest Ruby.

Backport the workflow to 5.0-stable and 3.19-stable before future release tags. The latter also needs the unprefixed tag pattern. Existing tags are not moved or republished by this change.

[Odilhao]

Why can't we keep using the voxpupuli one as we use in all other repos? We need to fix the gemspec to make it work.

[ogajduse]

The gemspec lists man/hammer.1.gz because it needs to ship in the gem, but that file must be generated before gem build. Removing it would make the build pass while dropping the man page.

I raised this in voxpupuli/ruby-release#13, where ekohl suggested starting with a longer Hammer-specific workflow that separates building from publishing. This PR follows that approach, keeping build steps outside the job with publishing permissions. I prefer shared tooling too, but we’d need support for generated files or a prebuilt gem, not just a gemspec change.