fix UpdateSettingsRequestStreamableTests.mutateInstance (elastic#39386)…

… (elastic#39477)

Mutations of the timeout values were using string-representations.

This resulted in very rare cases where the original timeout value was
represented as something like "0ms" and the new random time-value generated
was "0s". Although their string representations differ, their underlying
TimeValue does not. This resulted in `-Dtests.seed=7F4C034C43C22B1B` to
fail.

server/src/test/java/org/elasticsearch/action/admin/indices/settings/put/UpdateSettingsRequestStreamableTests.java

@@ -22,6 +22,7 @@
 import org.elasticsearch.action.support.IndicesOptions;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.settings.Settings.Builder;
+import org.elasticsearch.common.unit.TimeValue;
 import org.elasticsearch.common.util.CollectionUtils;
 import org.elasticsearch.test.AbstractStreamableTestCase;
 import org.elasticsearch.test.ESTestCase;
@@ -32,16 +33,18 @@
 import java.util.Locale;
 import java.util.Set;
 import java.util.StringJoiner;
+import java.util.function.Supplier;
 
 public class UpdateSettingsRequestStreamableTests extends AbstractStreamableTestCase<UpdateSettingsRequest> {
 
     @Override
     protected UpdateSettingsRequest mutateInstance(UpdateSettingsRequest request) {
         UpdateSettingsRequest mutation = copyRequest(request);
         List<Runnable> mutators = new ArrayList<>();
+        Supplier<TimeValue> timeValueSupplier = () -> TimeValue.parseTimeValue(ESTestCase.randomTimeValue(), "_setting");
         mutators.add(() -> mutation
-                .masterNodeTimeout(randomValueOtherThan(request.masterNodeTimeout().getStringRep(), ESTestCase::randomTimeValue)));
-        mutators.add(() -> mutation.timeout(randomValueOtherThan(request.timeout().getStringRep(), ESTestCase::randomTimeValue)));
+                .masterNodeTimeout(randomValueOtherThan(request.masterNodeTimeout(), timeValueSupplier)));
+        mutators.add(() -> mutation.timeout(randomValueOtherThan(request.timeout(), timeValueSupplier)));
         mutators.add(() -> mutation.settings(mutateSettings(request.settings())));
         mutators.add(() -> mutation.indices(mutateIndices(request.indices())));
         mutators.add(() -> mutation.indicesOptions(randomValueOtherThan(request.indicesOptions(),