Fix Docusaurus versioning error in publish_website workflow

Summary:
Fix Docusaurus versioning error when release workflow is re-run

## Problem
The 'Create new docusaurus version' step in publish_website.yml fails with:
```
Error: [docs]: this version already exists! Use a version tag that does not already exist.
```

This occurs when the release workflow is re-run for the same version (e.g., after a partial failure or manual re-trigger), because the version was already created and pushed to gh-pages in a previous run.

## Solution
Make the versioning step idempotent by checking if the version already exists in versions.json before attempting to create it:

1. Extract the version tag and remove the optional 'v' prefix
2. Check if versions.json exists and contains the version
3. Skip versioning if the version already exists, otherwise proceed normally

This allows the workflow to be safely re-run without failing.

Differential Revision: D95305476

Author: sdaulton

.github/workflows/publish_website.yml

@@ -86,11 +86,19 @@ jobs:
         python3 scripts/convert_ipynb_to_mdx.py --clean
         cd website
         yarn
-        yarn docusaurus docs:version ${{ inputs.new_version }}
 
-        git add versioned_docs/ versioned_sidebars/ versions.json
-        git commit -m "Create version ${{ inputs.new_version }} of site in Docusaurus"
-        git push --force origin HEAD:gh-pages
+        # Check if this version already exists in versions.json
+        VERSION_TAG="${{ inputs.new_version }}"
+        VERSION_TAG="${VERSION_TAG#v}"  # Remove optional "v" prefix for comparison
+        if [ -f versions.json ] && grep -q "\"$VERSION_TAG\"" versions.json; then
+          echo "Version $VERSION_TAG already exists in versions.json, skipping versioning step"
+        else
+          yarn docusaurus docs:version ${{ inputs.new_version }}
+
+          git add versioned_docs/ versioned_sidebars/ versions.json
+          git commit -m "Create version ${{ inputs.new_version }} of site in Docusaurus"
+          git push --force origin HEAD:gh-pages
+        fi
     - name: Build website
       run: |
         bash scripts/build_docs.sh -b