cmd/go: fix testdata/script/mod_vendor_goversion for new compiler output

The message is now a single line, but I couldn't get '\n?' to work.

(This test does not run in short mode.)

Change-Id: I3d7033f78ac2bf41db7fdfe96cbb988c4533d834
Reviewed-on: https://go-review.googlesource.com/c/go/+/359095
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>
diff --git a/src/cmd/go/testdata/script/mod_vendor_goversion.txt b/src/cmd/go/testdata/script/mod_vendor_goversion.txt
index b4489da..a92eb73 100644
--- a/src/cmd/go/testdata/script/mod_vendor_goversion.txt
+++ b/src/cmd/go/testdata/script/mod_vendor_goversion.txt
@@ -3,7 +3,6 @@
 
 [short] skip
 
-
 # Control case: without a vendor directory, need117 builds and bad114 doesn't.
 
 go build example.net/need117
@@ -26,7 +25,8 @@
 
 ! grep 1.17 vendor/modules.txt
 ! go build example.net/need117
-stderr '^vendor[/\\]example\.net[/\\]need117[/\\]need117.go:5:1[89]:.*\n\tconversion of slices to array pointers only supported as of -lang=go1\.17'
+stderr '^vendor[/\\]example\.net[/\\]need117[/\\]need117.go:5:1[89]:'
+stderr 'conversion of slices to array pointers only supported as of -lang=go1\.17'
 
 ! grep 1.13 vendor/modules.txt
 go build example.net/bad114