windows: fix parsing of non-ASCII entries in token.Environ

Fixes golang/go#65055, the unexpected behavior of token.Environ in parsing entries containing runes larger than 2 bytes in size

Change-Id: I753d2c605e3a2d7a1d90cd18601d6b918f0d3f7a
Reviewed-on: https://go-review.googlesource.com/c/sys/+/556895
Auto-Submit: Bryan Mills <bcmills@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
Reviewed-by: Quim Muntal <quimmuntal@gmail.com>

windows/env_windows_test.go

@@ -0,0 +1,40 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package windows_test
+
+import (
+	"fmt"
+	"slices"
+	"testing"
+
+	"golang.org/x/sys/windows"
+)
+
+func TestEnvironUTF8(t *testing.T) {
+	testEnvVariable1Key := "__GO_X_SYS_WINDOWS_ENV_WINDOWS_TEST_VAR_BEAVER"
+	testEnvVariable1Val := "🦫"
+	t.Setenv(testEnvVariable1Key, testEnvVariable1Val)
+
+	testEnvVariable2Key := "__GO_X_SYS_WINDOWS_ENV_WINDOWS_TEST_VAR_WHALE"
+	testEnvVariable2Val := "🐳"
+	t.Setenv(testEnvVariable2Key, testEnvVariable2Val)
+
+	var userToken windows.Token
+
+	env, err := userToken.Environ(true)
+	if err != nil {
+		t.Error(err)
+	}
+
+	testEnvVariable1 := fmt.Sprintf("%s=%s", testEnvVariable1Key, testEnvVariable1Val)
+	if !slices.Contains(env, testEnvVariable1) {
+		t.Fatalf("expected to find %s in env", testEnvVariable1)
+	}
+
+	testEnvVariable2 := fmt.Sprintf("%s=%s", testEnvVariable2Key, testEnvVariable2Val)
+	if !slices.Contains(env, testEnvVariable2) {
+		t.Fatalf("expected to find %s in env", testEnvVariable2)
+	}
+}