[ci] Use correct revision for Meta builds (facebook#32680)

There was a bug previously in our commit artifacts step where the
emitted REVISION hash would reference the commit on the builds branch
rather than from `main`.

Given that our internal manual sync script also does this, let's align
them both to always reference the commit from `main` instead.
---
[//]: # (BEGIN SAPLING FOOTER)
Stack created with [Sapling](https://sapling-scm.com). Best reviewed
with [ReviewStack](https://reviewstack.dev/facebook/react/pull/32680).
* __->__ facebook#32680
* facebook#32679
* facebook#32678

Author: poteto

.github/workflows/runtime_commit_artifacts.yml

@@ -151,9 +151,9 @@ jobs:
           ls -R ./compiled-rn
       - name: Add REVISION files
         run: |
-          echo ${{ github.sha }} >> ./compiled/facebook-www/REVISION
+          echo ${{ inputs.commit_sha || github.event.workflow_run.head_sha || github.sha }} >> ./compiled/facebook-www/REVISION
           cp ./compiled/facebook-www/REVISION ./compiled/facebook-www/REVISION_TRANSFORMS
-          echo ${{ github.sha}} >> ./compiled-rn/facebook-fbsource/xplat/js/react-native-github/Libraries/Renderer/REVISION
+          echo ${{ inputs.commit_sha || github.event.workflow_run.head_sha || github.sha }} >> ./compiled-rn/facebook-fbsource/xplat/js/react-native-github/Libraries/Renderer/REVISION
       - name: "Get current version string"
         id: get_current_version
         run: |