update to build docs for latest release

.github/workflows/build-docs.yml

@@ -1,7 +1,7 @@
 name: 'docs-publish'
 on:
   push:
-    branches: [ master ]
+    branches: [ rel-* ]
     paths:
         - 'docs/**'
   workflow_dispatch:
@@ -24,6 +24,22 @@ jobs:
     steps:
       - name: Checkout
         uses: actions/checkout@v4
+      - name: Determine latest rel-x.y branch
+        id: latest
+        run: |
+          latest_branch=$(git branch -r \
+            | sed 's|origin/||' \
+            | grep '^rel-[0-9]\+\.[0-9]\+$' \
+            | sed 's/rel-//' \
+            | sort -V \
+            | tail -n 1)
+          echo "latest=rel-$latest_branch" >> "$GITHUB_OUTPUT"
+
+      - name: Stop if not latest
+        if: steps.latest.outputs.latest != github.ref_name
+        run: |
+          echo "Not latest branch. This is ${{ github.ref_name }}, latest is ${{ steps.latest.outputs.latest }}"
+          exit 0
       - name: Setup bun
         uses: oven-sh/setup-bun@v2
         with: