test: fix unreliable test-fs-write-file.js

The test uses a file name twice, causing unreliability in CI. In
particular, it's failing a lot on the Raspberry Pi devices.

Fixes: #36090

PR-URL: #36102
Backport-PR-URL: #38386
Reviewed-By: Luigi Pinca <[email protected]>
Reviewed-By: Richard Lau <[email protected]>

Author: Trott

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

@@ -88,7 +88,7 @@ fs.open(filename4, 'w+', common.mustSucceed((fd) => {
   // After the operation has started
   const controller = new AbortController();
   const signal = controller.signal;
-  const filename4 = join(tmpdir.path, 'test4.txt');
+  const filename4 = join(tmpdir.path, 'test5.txt');
 
   fs.writeFile(filename4, s, { signal }, common.mustCall((err) => {
     assert.strictEqual(err.name, 'AbortError');