gopls/test: disable stderr output for command line tests as well

Suppress output in gopls command line tests, similarly to CL 431843.

For golang/go#54845

Change-Id: I7f1e1de52c9a8fb0d902bfdd61bc99d4e2e308b9
Reviewed-on: https://go-review.googlesource.com/c/tools/+/432955
Reviewed-by: Alan Donovan <adonovan@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
gopls-CI: kokoro <noreply+kokoro@google.com>

gopls/test/gopls_test.go

@@ -13,12 +13,20 @@ import (
 	"golang.org/x/tools/gopls/internal/lsp/source"
 	"golang.org/x/tools/gopls/internal/lsp/tests"
 	"golang.org/x/tools/internal/bug"
+	"golang.org/x/tools/internal/event"
 	"golang.org/x/tools/internal/testenv"
 )
 
 func TestMain(m *testing.M) {
 	bug.PanicOnBugs = true
 	testenv.ExitIfSmallMachine()
+
+	// Set the global exporter to nil so that we don't log to stderr. This avoids
+	// a lot of misleading noise in test output.
+	//
+	// See also ../internal/lsp/lsp_test.go.
+	event.SetExporter(nil)
+
 	os.Exit(m.Run())
 }