test: mark some GC-related tests as flaky

Refs: #52273
PR-URL: #51362
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Rafael Gonzaga <rafael.nunu@hotmail.com>

test/parallel/parallel.status

@@ -5,6 +5,10 @@ prefix parallel
 # sample-test                        : PASS,FLAKY
 
 [true] # This section applies to all platforms
+# https://github.com/nodejs/node/issues/52273
+test-net-write-fully-async-hex-string: PASS, FLAKY
+test-shadow-realm-gc: PASS, FLAKY
+test-shadow-realm-gc-module: PASS, FLAKY
 
 [$system==win32]