test/fixedbugs: fix issue48784.go to pass with -G=0

This test is currently failing in the longtest builders.

I do not know how or why the builders are adding the -G=0 parameter.

Updates #48784

Change-Id: I62248d3fbc47567a8c73b4868a2d4aeb0bc47bc3
Reviewed-on: https://go-review.googlesource.com/c/go/+/354631


Trust: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Robert Griesemer <gri@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>