test: improve test-fs-open

If there is a file 'path' in the root dir, the test
will fail with the 'ENOTDIR' instead of 'ENOENT'.
Change path to something more unlikely.

PR-URL: https://github.com/nodejs/node/pull/30280
Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>

test/parallel/test-fs-open.js

@@ -29,7 +29,7 @@ let caughtException = false;
 try {
   // Should throw ENOENT, not EBADF
   // see https://github.com/joyent/node/pull/1228
-  fs.openSync('/path/to/file/that/does/not/exist', 'r');
+  fs.openSync('/8hvftyuncxrt/path/to/file/that/does/not/exist', 'r');
 } catch (e) {
   assert.strictEqual(e.code, 'ENOENT');
   caughtException = true;