Fix rare serialization failure in SuggestTests (elastic#101014)

SuggestTests uses a fairly recursive way to create its test item. Those can end
up with an CompletionSuggestion.Entry.Option that have a "rank" field set to
something other than the bwc default of -1. The test still tries to test the
serialization roundtrip to a random transport version down to TransportVersions.MINIMUM_COMPATIBLE
which is currently at V_7_17_0, but the rank field serialization fails for
anything below V_8_8_0. In reality however, suggester options shouldn't contain search
hits with a set rank field, so simples way to avoid it is checking the randomly
created test item for those cases and correct them before running the test.

Closes elastic#95607

server/src/test/java/org/elasticsearch/search/suggest/SuggestTests.java

@@ -239,7 +239,6 @@ public void testMergingSuggestionOptions() {
         assertTrue(option1.collateMatch());
     }
 
-    @AwaitsFix(bugUrl = "https://github.com/elastic/elasticsearch/issues/95607")
     public void testSerialization() throws IOException {
         TransportVersion bwcVersion = TransportVersionUtils.randomVersionBetween(
             random(),
@@ -248,6 +247,22 @@ public void testSerialization() throws IOException {
         );
 
         final Suggest suggest = createTestItem();
+        // suggest is disallowed when using rank, but the randomization rarely sets it
+        // we need to make sure CompletionSuggestion$Entry$Option doesn't have "rank" set
+        // because for some older versions it will not serialize.
+        if (bwcVersion.before(TransportVersions.V_8_8_0)) {
+            for (CompletionSuggestion s : suggest.filter(CompletionSuggestion.class)) {
+                for (CompletionSuggestion.Entry entry : s.entries) {
+                    List<CompletionSuggestion.Entry.Option> options = entry.getOptions();
+                    for (CompletionSuggestion.Entry.Option o : entry.getOptions()) {
+                        if (o.getHit() != null) {
+                            o.getHit().setRank(-1);
+                        }
+                    }
+                }
+            }
+        }
+
         final Suggest bwcSuggest;
 
         NamedWriteableRegistry registry = new NamedWriteableRegistry(new SearchModule(Settings.EMPTY, emptyList()).getNamedWriteables());