test: fix test issue 69434 for riscv64

test: fix test issue 69434 for riscv64

CL 615915 simplified test for issue 69434, using gcflags maymorestack to
force stack moving, making program failed with invalid stack pointer.

However, it seems that this maymorestack is broken on riscv64. At least
gotip-linux-riscv64 is currently broken.

This CL fixes this problem by using the initial approach, growing stack
size big enough to force stack moving.

Updates #69434
Fixes #69714

Cq-Include-Trybots: luci.golang.try:gotip-linux-riscv64
Change-Id: I95255fba884a200f75bcda34d58e9717e4a952ad
Reviewed-on: https://go-review.googlesource.com/c/go/+/616698
Reviewed-by: Keith Randall <khr@google.com>
Auto-Submit: Cuong Manh Le <cuong.manhle.vn@gmail.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: David Chase <drchase@google.com>