Tentative workflow improvement (#15255)

.github/workflows/build_dev_documentation.yml

@@ -35,12 +35,30 @@ jobs:
 
       - name: Comment PR
         uses: thollander/actions-comment-pull-request@v1
-        if: github.event.action == 'opened' || github.event.action == 'reopened'
+        if: github.event.action == 'opened'
 
         with:
-          message: 'Thank you for your PR! The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_${{ env.PR_NUMBER }}). All of your documentation changes will be reflected on that endpoint.'
+          message: 'The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_${{ env.PR_NUMBER }}). All of your documentation changes will be reflected on that endpoint.'
           GITHUB_TOKEN: ${{ env.WRITE }}
 
+      - name: Find Comment
+        if: github.event.action == 'reopened'
+        uses: peter-evans/find-comment@v1
+        id: fc
+        with:
+          issue-number: ${{ env.PR_NUMBER }}
+          comment-author: HuggingFaceDocBuilder
+
+      - name: Update comment
+        if: github.event.action == 'reopened'
+        uses: peter-evans/create-or-update-comment@v1
+        with:
+          comment-id: ${{ steps.fc.outputs.comment-id }}
+          token: ${{ env.WRITE }}
+          edit-mode: replace
+          body: |
+            The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_${{ env.PR_NUMBER }}). All of your documentation changes will be reflected on that endpoint.
+
       - name: Loading cache.
         uses: actions/cache@v2
         id: cache