[llvm] AMDGPU: Stop running assembler tests with default cpu (PR #117421)

[Matt Arsenault via llvm-commits]

arsenm wrote:

### Merge activity

* **Nov 23, 12:16 PM EST**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/117421).


https://github.com/llvm/llvm-project/pull/117421