Auto-create draft releases when building release tags (#2275)

Update the CI so that it drafts a release, with the correct artifacts attached
and the release notes prepared, when building a release tag.

.github/workflows/main.yml

@@ -243,6 +243,14 @@ jobs:
     name: "🔎 Validate generated HTML"
     runs-on: ubuntu-latest
     needs: [calculate-baseurl, build-spec]
+    # Run even if `generate-changelog` was skipped.
+    #
+    # `build-spec` has a dependency on `generate-changelog` to ensure order of execution
+    # and to access `needs.generate-changelog.result`. However, `generate-changelog` is
+    # skipped on tag builds; even a transient dependency on `generate-changelog` is then
+    # enough for this step to also be skipped by default on tag builds. Hence the need for
+    # this explicit `if`.
+    if: ${{ !failure() && !cancelled() }}
     steps:
       - name: "📥 Source checkout"
         uses: actions/checkout@v4
@@ -305,8 +313,45 @@ jobs:
 
       - name: "📦 Tarball creation"
         run: tar -czf spec-historical.tar.gz spec
+
       - name: "📤 Artifact upload"
         uses: actions/upload-artifact@v4
         with:
           name: spec-historical-artifact
           path: spec-historical.tar.gz
+
+  # If we're building a tag, create a release and publish the artifacts
+  create_release:
+    name: "Create release"
+    if: ${{ !failure() && !cancelled() && startsWith(github.ref, 'refs/tags/') }}
+    needs:
+      - build-spec
+      - build-historical-spec
+    runs-on: ubuntu-latest
+    steps:
+      - name: "📥 Check out changelogs"
+        uses: actions/checkout@1af3b93b6815bc44a9784bd300feb67ff0d1eeb3 # v6.0.0
+        with:
+          sparse-checkout: |
+            content/changelog
+      - name: "📥 Download built spec"
+        uses: actions/download-artifact@37930b1c2abaa49bbe596cd826c3c89aef350131 # v7.0.0
+        with:
+          name: spec-artifact
+      - name: "📥 Download historical spec artifact"
+        uses: actions/download-artifact@37930b1c2abaa49bbe596cd826c3c89aef350131 # v7.0.0
+        with:
+          name: spec-historical-artifact
+      - name: "✨ Create draft release"
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          # Remove front-matter from changelog
+          sed '1,/^---$/d' "content/changelog/${{ github.ref_name }}.md" > changelog.md
+
+          # Create a draft release, using the changelog as release notes, and attaching the spec artifacts.
+          gh release create -d -t "${{ github.ref_name }}" \
+            -F "changelog.md" \
+            "${{ github.ref_name }}" \
+            spec.tar.gz \
+            spec-historical.tar.gz

changelogs/internal/newsfragments/2275.clarification

@@ -0,0 +1 @@
+Auto-create draft releases when building release tags.