I really think github.event.issue should be github.event.pull_request...

.github/workflows/generate_api_docs.yaml

@@ -29,7 +29,7 @@ jobs:
       - name: "Get PR Info"
         id: pr
         env:
-          PR_NUMBER: ${{ github.event.issue.number }}
+          PR_NUMBER: ${{ github.event.pull_request.number }}
           GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
           GH_REPO: ${{ github.repository }}
           COMMENT_AT: ${{ github.event.comment.created_at }}
@@ -48,7 +48,7 @@ jobs:
       - name: Checkout the branch from the PR that triggered the job
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-        run: gh pr checkout ${{ github.event.issue.number }}
+        run: gh pr checkout ${{ github.event.pull_request.number }}
 
       - name: Validate the fetched branch HEAD revision
         env: