[TESTING] Add golden sample test for pipelining matmul with descripto…

…rs (#5289)

<git-pr-chain>


[TESTING] Add golden sample test for pipelining matmul with descriptors


#### [PR chain](https://github.com/jlebar/git-pr-chain)
1. #5288
1. 👉 #5289 👈 **YOU ARE HERE**
1. #5290

⚠️⚠️ Please **do not click the green "merge" button** unless you know
what
you're doing.  This PR is part of a chain of PRs, and clicking the merge
button will not merge it into master. ⚠️⚠️ 
</git-pr-chain>