Fix input snapshotting error when using test clusters cliSetup (#52340)

Author: mark-vieira

buildSrc/src/main/java/org/elasticsearch/gradle/LazyPropertyList.java

@@ -170,13 +170,23 @@ public List<T> subList(int fromIndex, int toIndex) {
     }
 
     @Override
-    public List<? extends Object> getNormalizedCollection() {
+    public List<? extends PropertyListEntry<T>> getNormalizedCollection() {
         return delegate.stream()
             .peek(this::validate)
             .filter(entry -> entry.getNormalization() != PropertyNormalization.IGNORE_VALUE)
             .collect(Collectors.toList());
     }
 
+    /**
+     * Return a "flattened" collection. This should be used when the collection type is itself a complex type with properties
+     * annotated as Gradle inputs rather than a simple type like {@link String}.
+     *
+     * @return a flattened collection filtered according to normalization strategy
+     */
+    public List<? extends T> getFlatNormalizedCollection() {
+        return getNormalizedCollection().stream().map(PropertyListEntry::getValue).collect(Collectors.toList());
+    }
+
     private void validate(PropertyListEntry<T> entry) {
         assertNotNull(entry.getValue(), "entry");
     }

buildSrc/src/main/java/org/elasticsearch/gradle/testclusters/ElasticsearchNode.java

@@ -1188,7 +1188,7 @@ public List<?> getKeystoreFiles() {
 
     @Nested
     public List<?> getCliSetup() {
-        return cliSetup.getNormalizedCollection();
+        return cliSetup.getFlatNormalizedCollection();
     }
 
     @Nested