Figure out failed playwright report merger

[TomStrepsil]

Issue

The "Playwright Report Merger" step of the automation tests seems ineffective.

Details

Similar symptoms to microsoft/playwright#31417

Sometimes, get:

Warning: No files were found with the provided path: playwright-report. No artifacts will be uploaded.

...when trying to upload. Other times, the merge only contains one shard. In other cases receives:

Error: not enough bytes in the stream. expected 331585. got only 298452

...during upload