Preserve PyTest Cache across job runs (#100522)
Preserves the PyTest cache from one job run to the next. In a later PR, this will be used to change the order in which we actually run those tests
The process is:
1. Before running tests, check S3 to see if there is an uploaded cache from any shard of the current job
2. If there are, download them all and merge their contents. Put the merged cache in the default .pytest_cache folder
3. After running the tests, merge the now-current .pytest_cache folder with the cache previously downloaded for the current shard. This will make the merged cache contain all tests that have ever failed for the given PR in the current shard
4. Upload the resulting cache file back to S3
The S3 folder has a retention policy of 30 days, after which the uploaded cache files will get auto-deleted.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/100522
Approved by: https://github.com/huydhn
