test: fix flaky async-hooks/test-zlib.zlib-binding.deflate

Previously, the typed arrays used in this test would not
automatically be kept alive by the native handle when
it’s using them, so the V8 garbage collector could collect
them while they are still in use by the zlib module,
leading to memory corruption.

Fixes: #20907

test/async-hooks/test-zlib.zlib-binding.deflate.js

@@ -21,31 +21,37 @@ assert.strictEqual(typeof hdl.uid, 'number');
 assert.strictEqual(typeof hdl.triggerAsyncId, 'number');
 checkInvocations(hdl, { init: 1 }, 'when created handle');
 
+// Store all buffers together so that they do not get
+// garbage collected.
+const buffers = {
+  writeResult: new Uint32Array(2),
+  dictionary: new Uint8Array(0),
+  inBuf: new Uint8Array([0x78]),
+  outBuf: new Uint8Array(1)
+};
+
 handle.init(
   constants.Z_DEFAULT_WINDOWBITS,
   constants.Z_MIN_LEVEL,
   constants.Z_DEFAULT_MEMLEVEL,
   constants.Z_DEFAULT_STRATEGY,
-  new Uint32Array(2),
+  buffers.writeResult,
   function processCallback() { this.cb(); },
-  Buffer.from('')
+  buffers.dictionary
 );
 checkInvocations(hdl, { init: 1 }, 'when initialized handle');
 
-const inBuf = Buffer.from('x');
-const outBuf = Buffer.allocUnsafe(1);
-
 let count = 2;
 handle.cb = common.mustCall(onwritten, 2);
-handle.write(true, inBuf, 0, 1, outBuf, 0, 1);
+handle.write(true, buffers.inBuf, 0, 1, buffers.outBuf, 0, 1);
 checkInvocations(hdl, { init: 1 }, 'when invoked write() on handle');
 
 function onwritten() {
   if (--count) {
     // first write
     checkInvocations(hdl, { init: 1, before: 1 },
                      'when wrote to handle the first time');
-    handle.write(true, inBuf, 0, 1, outBuf, 0, 1);
+    handle.write(true, buffers.inBuf, 0, 1, buffers.outBuf, 0, 1);
   } else {
     // second write
     checkInvocations(hdl, { init: 1, before: 2, after: 1 },
@@ -61,4 +67,7 @@ function onexit() {
   // TODO: destroy never called here even with large amounts of ticks
   // is that correct?
   checkInvocations(hdl, { init: 1, before: 2, after: 2 }, 'when process exits');
+
+  // Do something with `buffers` to keep them alive until here.
+  buffers.buffers = buffers;
 }