test/codegen: make sure assignment results are used.
Some tests make assignments to an argument without reading it.
With CL 708865, they are treated as dead stores and are removed.
Make sure the results are used.
Fixes #75745.
Fixes #75746.
Change-Id: I05580beb1006505ec1550e5fa245b54dcefd10b9
Reviewed-on: https://go-review.googlesource.com/c/go/+/708916
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Keith Randall <khr@google.com> Reviewed-by: Keith Randall <khr@golang.org>