devops: call merge-reports with explicit config (#27965)

After https://github.com/microsoft/playwright/pull/27963 we have to
provide explicit merge config to disambiguate testDir.

.github/workflows/create_test_report.yml

@@ -31,7 +31,7 @@ jobs:
 
     - name: Merge reports
       run: |
-        npx playwright merge-reports --reporter markdown,html ./all-blob-reports
+        npx playwright merge-reports --config .github/workflows/merge.config.ts ./all-blob-reports
       env:
         NODE_OPTIONS: --max-old-space-size=4096
 

.github/workflows/merge.config.ts

@@ -0,0 +1,4 @@
+export default {
+  testDir: '../../tests',
+  reporter: [['markdown'], ['html']]
+};