CI: Fix flaky artifact upload step (#121733)
This PR changes the upload artifact step of the wheels and conda build to write
each matrix entry to a different file. This is because updating the same file
from multiple jobs can be flaky as is warned in the docs for upload-artifact
> Warning: Be careful when uploading to the same artifact via multiple jobs as artifacts may become corrupted. When uploading a file with an identical name and path in multiple jobs, uploads may fail with 503 errors due to conflicting uploads happening at the same time. Ensure uploads to identical locations to not interfere with each other.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/121733
Approved by: https://github.com/huydhn
ghstack dependencies: #121268
