cmd/go: fix long test builders

CL 343732 enabled -G=3 by default. The types2 typechecker uses slighly
different error message format for language feature constraint.

The old typechecker format:

	vendor/example.net/need117/need117.go:5:16: cannot convert s (type []byte) to type *[4]byte:
		conversion of slices to array pointers only supported as of -lang=go1.17

The new format:

	vendor/example.net/need117/need117.go:5:17: conversion of slices to array pointers only supported as of -lang=go1.17

caused the long test builders failed.

This CL fixes the test by relaxing the regext pattern a bit, so it can
match both the format.

Change-Id: I1c4acaa9e34b6c08dccbbc3ce7a99d4cd79f748a
Reviewed-on: https://go-review.googlesource.com/c/go/+/344212


Trust: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>