gopls/internal/test/integration/workspace: fix TestStdWorkspace

When finding GOROOT for TestStdWorkspace, set GOTOOLCHAIN=local to avoid
toolchain upgrades due to the gopls go.mod file.

Fixes golang/go#70187

Change-Id: I151b4f5a39e6f71a6d4df0742a9d5a77060285e5
Reviewed-on: https://go-review.googlesource.com/c/tools/+/625116
Auto-Submit: Robert Findley <rfindley@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Alan Donovan <adonovan@google.com>

Author: findleyr

gopls/internal/test/integration/workspace/std_test.go

@@ -5,6 +5,7 @@
 package workspace
 
 import (
+	"os"
 	"os/exec"
 	"path/filepath"
 	"runtime"
@@ -36,7 +37,12 @@ func TestStdWorkspace(t *testing.T) {
 
 	// Query GOROOT. This is slightly more precise than e.g. runtime.GOROOT, as
 	// it queries the go command in the environment.
-	goroot, err := exec.Command("go", "env", "GOROOT").Output()
+	cmd := exec.Command("go", "env", "GOROOT")
+	// Run with GOTOOLCHAIN=local so as to not be affected by toolchain upgrades
+	// in the current directory (which is affected by gopls' go.mod file).
+	// This was golang/go#70187
+	cmd.Env = append(os.Environ(), "GOTOOLCHAIN=local")
+	goroot, err := cmd.Output()
 	if err != nil {
 		t.Fatal(err)
 	}