fix: Use head_commit_sha in authorize-vercel-deploys.yml action (#41795)

* Use head commit sha in the authorize-vercel-deploys.yml.

* Add comments.

.github/workflows/authorize-vercel-deploys.yml

@@ -1,5 +1,7 @@
 name: Authorize Vercel Deploys
 
+# This workflow is triggered by the validate-pr workflow. When it's triggered, it will run the
+# authorize-vercel-deploys.yml in master branch. If you want to change it, you'll have to merge it into master.
 on:
   # only run this workflow when the validate-pr workflow completes (successfully or not)
   workflow_run:
@@ -44,3 +46,5 @@ jobs:
           pnpm run authorize-vercel-deploys
         env:
           VERCEL_TOKEN: ${{ secrets.VERCEL_TOKEN }}
+          # The SHA of the commit that triggered the validate-pr workflow
+          HEAD_COMMIT_SHA: ${{ github.event.workflow_run.head_sha }}

.github/workflows/validate-pr.yml

@@ -1,5 +1,6 @@
 name: Validate pull request
 
+# This workflow will trigger the authorize-vercel-deploys workflow when it's finished.
 on:
   pull_request:
     types: [opened, labeled, unlabeled, synchronize, ready_for_review]

scripts/authorizeVercelDeploys.ts

@@ -91,9 +91,9 @@ async function authorizeVercelJob(jobInfo: JobInfo, vercelToken: string): Promis
 }
 
 async function main() {
-  const sha = process.env.GITHUB_SHA
+  const sha = process.env.HEAD_COMMIT_SHA
   if (!sha) {
-    throw new Error('GITHUB_SHA environment variable is required')
+    throw new Error('HEAD_COMMIT_SHA environment variable is required')
   }
 
   const vercelToken = process.env.VERCEL_TOKEN