cmd/go/testdata/script: fix test script added by CL 334873

cmd/go/testdata/script: fix test script added by CL 334873

CL 334873 added the net/http import to the wrong section in
test_vet.txt. Correct this to fix the longtest builders.

Change-Id: If28409ad1c2ed3bd3a2922fc20d5e534c30fa249
Reviewed-on: https://go-review.googlesource.com/c/go/+/343169
Trust: Tobias Klauser <tobias.klauser@gmail.com>
Trust: Jay Conrod <jayconrod@google.com>
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>