[Tests] node v21.3 has a broken fs.writeFile

See nodejs/node#50990 / nodejs/node#50989

Author: ljharb

tests/src/rules/no-unused-modules.js

@@ -732,7 +732,7 @@ describe('renameDefault', () => {
 
 describe('test behavior for new file', () => {
   before(() => {
-    fs.writeFileSync(testFilePath('./no-unused-modules/file-added-0.js'), '', { encoding: 'utf8' });
+    fs.writeFileSync(testFilePath('./no-unused-modules/file-added-0.js'), '', { encoding: 'utf8', flag: 'w' });
   });
 
   // add import in newly created file
@@ -840,7 +840,7 @@ describe('test behavior for new file', () => {
 
   describe('test behavior for new file', () => {
     before(() => {
-      fs.writeFileSync(testFilePath('./no-unused-modules/file-added-1.js'), '', { encoding: 'utf8' });
+      fs.writeFileSync(testFilePath('./no-unused-modules/file-added-1.js'), '', { encoding: 'utf8', flag: 'w' });
     });
     ruleTester.run('no-unused-modules', rule, {
       valid: [
@@ -875,7 +875,7 @@ describe('test behavior for new file', () => {
 
 describe('test behavior for new file', () => {
   before(() => {
-    fs.writeFileSync(testFilePath('./no-unused-modules/file-added-2.js'), '', { encoding: 'utf8' });
+    fs.writeFileSync(testFilePath('./no-unused-modules/file-added-2.js'), '', { encoding: 'utf8', flag: 'w' });
   });
   ruleTester.run('no-unused-modules', rule, {
     valid: [
@@ -901,7 +901,7 @@ describe('test behavior for new file', () => {
 
 describe('test behavior for new file', () => {
   before(() => {
-    fs.writeFileSync(testFilePath('./no-unused-modules/file-added-3.js'), '', { encoding: 'utf8' });
+    fs.writeFileSync(testFilePath('./no-unused-modules/file-added-3.js'), '', { encoding: 'utf8', flag: 'w' });
   });
   ruleTester.run('no-unused-modules', rule, {
     valid: [
@@ -952,7 +952,7 @@ describe('test behavior for destructured exports', () => {
 
 describe('test behavior for new file', () => {
   before(() => {
-    fs.writeFileSync(testFilePath('./no-unused-modules/file-added-4.js.js'), '', { encoding: 'utf8' });
+    fs.writeFileSync(testFilePath('./no-unused-modules/file-added-4.js.js'), '', { encoding: 'utf8', flag: 'w' });
   });
   ruleTester.run('no-unused-modules', rule, {
     valid: [