test: fix failure in test/sequential/test-heapdump.js

The test was failing when it was being run with superuser privileges,
so this changes the test from attempting to write to a read-only file to
attempting to write to a file with the same name as that of an existing
directory, as that is a more reliable way of making
v8.writeHeapSnapshot() throw even when run with sudo.

Fixes: #41643
Signed-off-by: Darshan Sen <raisinten@gmail.com>

PR-URL: #41772
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>

Author: RaisinTen

test/sequential/test-heapdump.js

@@ -25,13 +25,15 @@ process.chdir(tmpdir.path);
 }
 
 {
-  const readonlyFile = 'ro';
-  fs.writeFileSync(readonlyFile, Buffer.alloc(0), { mode: 0o444 });
+  const directory = 'directory';
+  fs.mkdirSync(directory);
   assert.throws(() => {
-    writeHeapSnapshot(readonlyFile);
+    writeHeapSnapshot(directory);
   }, (e) => {
     assert.ok(e, 'writeHeapSnapshot should error');
-    assert.strictEqual(e.code, 'EACCES');
+    // TODO(RaisinTen): This should throw EISDIR on Windows too.
+    assert.strictEqual(e.code,
+                       process.platform === 'win32' ? 'EACCES' : 'EISDIR');
     assert.strictEqual(e.syscall, 'open');
     return true;
   });