Fix bug where using a YAML with anchors couldn't be loaded

Closes gh-33404

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/env/OriginTrackedYamlLoader.java

@@ -79,7 +79,7 @@ private Yaml createYaml(LoaderOptions loaderOptions) {
 	}
 
 	List<Map<String, Object>> load() {
-		final List<Map<String, Object>> result = new ArrayList<>();
+		List<Map<String, Object>> result = new ArrayList<>();
 		process((properties, map) -> result.add(getFlattenedMap(map)));
 		return result;
 	}
@@ -119,7 +119,9 @@ protected Object constructObject(Node node) {
 		}
 
 		private void replaceMappingNodeKeys(MappingNode node) {
-			node.setValue(node.getValue().stream().map(KeyScalarNode::get).toList());
+			List<NodeTuple> newValue = new ArrayList<>();
+			node.getValue().stream().map(KeyScalarNode::get).forEach(newValue::add);
+			node.setValue(newValue);
 		}
 
 		private Object constructTrackedObject(Node node, Object value) {

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/env/OriginTrackedYamlLoaderTests.java

@@ -173,6 +173,15 @@ void loadWhenRecursiveLoadsYaml() {
 		assertThat(loaded.get("test.b.boot")).hasToString("b");
 	}
 
+	@Test
+	void loadWhenUsingAnchors() {
+		Resource resource = new ClassPathResource("anchors.yml", getClass());
+		this.loader = new OriginTrackedYamlLoader(resource);
+		Map<String, Object> loaded = this.loader.load().get(0);
+		assertThat(loaded.get("some.path.config.key")).hasToString("value");
+		assertThat(loaded.get("some.anotherpath.config.key")).hasToString("value");
+	}
+
 	private OriginTrackedValue getValue(String name) {
 		if (this.result == null) {
 			this.result = this.loader.load();

spring-boot-project/spring-boot/src/test/resources/org/springframework/boot/env/anchors.yml

@@ -0,0 +1,6 @@
+some:
+  path: &anchor
+    config:
+      key: value
+  anotherpath:
+    <<: *anchor