Meta: fix passing PR number (see #2260)

Author: ljharb

.github/workflows/preview-build.yml

@@ -7,9 +7,6 @@ jobs:
   build:
     name: 'build PR preview'
     runs-on: ubuntu-latest
-    outputs:
-      sha: ${{ github.event.pull_request.head.sha }}
-      pr: ${{ github.event.number }}
 
     steps:
       - uses: actions/checkout@v2
@@ -20,6 +17,7 @@ jobs:
           use-npm-ci: true
       - run: npm run build-only
       - run: node scripts/insert_snapshot_warning
+      - run: echo ${{ github.event.number }} > out/pr.txt
       - uses: actions/upload-artifact@v2
         with:
           name: out

.github/workflows/preview.yml

@@ -49,8 +49,9 @@ jobs:
         with:
           script: |
             console.log(${{ toJson(github.event) }});
+      - run: echo "PULL_REQUEST=$(cat out/pr.txt" >> $GITHUB_ENV
+      - run: rm out/pr.txt && echo $PULL_REQUEST
       - run: node scripts/publish-preview
         env:
           CI_PREVIEW_TOKEN: ${{ secrets.CI_PREVIEW_TOKEN }}
-          PULL_REQUEST: ${{ github.event.workflow_run.pull_requests['0'].number }}
           GITHUB_HEAD_SHA: ${{ github.event.workflow_run.head_commit.id }}