[stubs] Fix flaky failures of cctest/test-code-stub-assembler/SeededNumberDictionaryLookup.

test/cctest/test-code-stub-assembler.cc

Index: test/cctest/test-code-stub-assembler.cc
diff --git a/test/cctest/test-code-stub-assembler.cc b/test/cctest/test-code-stub-assembler.cc
index 6f4414e177648c0a8bc017aa9205af309c69c3f2..fff3c89e308a01655a20dc0365a5b98eb92f4eeb 100644
--- a/test/cctest/test-code-stub-assembler.cc
+++ b/test/cctest/test-code-stub-assembler.cc
@@ -696,6 +696,7 @@ void TestNumberDictionaryLookup() {
   for (int i = 0; i < kKeysCount; i++) {
     int random_key = rand_gen.NextInt(Smi::kMaxValue);
     keys[i] = static_cast<uint32_t>(random_key);
+    if (dictionary->FindEntry(keys[i]) != Dictionary::kNotFound) continue;
 
     dictionary = Dictionary::Add(dictionary, keys[i], fake_value, fake_details);
   }