gopls/internal/analysis/fillreturns: skip test if gotypesalias=1

It changes (improves) the behavior of the test; we will reenable
it once the default has changed.

Updates golang/go#65294

Change-Id: I716da405a9f0c03c303c4c0be8b738dd7c5ebdcd
Reviewed-on: https://go-review.googlesource.com/c/tools/+/576137
Reviewed-by: Tim King <taking@google.com>
Auto-Submit: Alan Donovan <adonovan@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

gopls/internal/analysis/fillreturns/fillreturns_test.go

@@ -5,13 +5,20 @@
 package fillreturns_test
 
 import (
+	"os"
+	"strings"
 	"testing"
 
 	"golang.org/x/tools/go/analysis/analysistest"
 	"golang.org/x/tools/gopls/internal/analysis/fillreturns"
 )
 
 func Test(t *testing.T) {
+	// TODO(golang/go#65294): delete once gotypesalias=1 is the default.
+	if strings.Contains(os.Getenv("GODEBUG"), "gotypesalias=1") {
+		t.Skip("skipping due to gotypesalias=1, which changes (improves) the result; reenable and update the expectations once it is the default")
+	}
+
 	testdata := analysistest.TestData()
 	analysistest.RunWithSuggestedFixes(t, testdata, fillreturns.Analyzer, "a", "typeparams")
 }