test: mark test-file-write-stream4 as flaky

The flake has been detected since 2021-10-30 and still has been
affecting recent PRs significantly (failing 8 PRs out of the
last 100 CI run up until 2025-04-18). The underlying cause
is still under investigation but in the meantime it's better
to mark it as a known flake to keep the CI functional.

Author: joyeecheung

test/parallel/parallel.status

@@ -12,6 +12,10 @@ test-shadow-realm-gc-module: SKIP
 # https://github.com/nodejs/node/issues/51862
 test-fs-read-stream-concurrent-reads: PASS, FLAKY
 
+# https://github.com/nodejs/node/issues/56883
+# Potentially caused by https://github.com/nodejs/node/issues/54918
+test-file-write-stream4: PASS, FLAKY
+
 # Until V8 provides a better way to check for flag mismatch without
 # making the code cache/snapshot unreproducible, disable the test
 # for a preemptive check now. It should ideally fail more gracefully