chore(deps): bump actions/github-script from 7 to 9

## Related Issue

No linked issue. This is an automated dependency update.

## Problem

The Nix workflow still uses `actions/github-script` v7.

## What changed

- Upgrade both Nix failure-comment steps to `actions/github-script` v9.
- Pin v9 to its reviewed commit SHA.
- Keep the workflow scripts and inputs unchanged.

## Checklist

- [x] I have read the
[CONTRIBUTING](https://github.com/PyModel/pythinker-code/blob/main/CONTRIBUTING.md)
document.
- [x] A related issue is not applicable to this automated dependency
update.
- [x] I validated the workflow YAML and both embedded scripts; required
CI checks validate the current head.
- [x] No changeset is needed because users cannot perceive this
workflow-only update.
- [x] No documentation update is needed.

---------

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: M Elkholy <melkholy@techmatrix.com>

Author: dependabot[bot]

.github/workflows/nix-build.yml

@@ -48,7 +48,7 @@ jobs:
 
       - name: Post or update PR comment
         if: steps.check.outputs.SYNC_OK == 'false' && github.event_name == 'pull_request'
-        uses: actions/github-script@v7
+        uses: actions/github-script@3a2844b7e9c422d3c10d287c895573f7108da1b3 # v9
         env:
           COMMENT_BODY: ${{ steps.missing.outputs.body }}
         with:
@@ -151,7 +151,7 @@ jobs:
 
       - name: Post or update PR comment
         if: steps.build.outputs.BUILD_FAILED == 'true' && github.event_name == 'pull_request'
-        uses: actions/github-script@v7
+        uses: actions/github-script@3a2844b7e9c422d3c10d287c895573f7108da1b3 # v9
         env:
           COMMENT_BODY: ${{ steps.error.outputs.body }}
         with: