test: cover mixed-case UTF-8 write aliases

Author: icecold009

test/parallel/test-fs-write-file-sync.js

@@ -122,7 +122,7 @@ tmpdir.refresh();
 // Test writeFileSync with UTF-8 encoding aliases
 {
   const utf8Data = 'hello world! 中文 — 🚀';
-  for (const encoding of ['utf8', 'utf-8', 'UTF8', 'UTF-8']) {
+  for (const encoding of ['utf8', 'utf-8', 'UTF8', 'UTF-8', 'Utf8', 'Utf-8']) {
     const file = tmpdir.resolve(`testWriteFileSyncEncoding_${encoding}.txt`);
     fs.writeFileSync(file, utf8Data, { encoding });
     assert.strictEqual(fs.readFileSync(file, 'utf8'), utf8Data);