[sparse] fix sparse_codegen_test_*
[sparse] fix sparse_codegen_test_*

Properly reenable string-stitching in the compilation flow. Mid-term, string
stitching should be replaced with proper IR construction from Python.

PiperOrigin-RevId: 399884405

iree-org/iree-llvm-sandbox,iree-org/iree-llvm-sandbox,iree-org/iree-llvm-sandbox,iree-org/iree-llvm-sandbox