fix java cdk utility tasks (airbytehq#34174)

these tasks were only checking within the cdk directory, so they didn't actually accomplish anything. Fix them to walk the entire tree.

... afaict we don't actually use these tasks for anything, but might as well make them work?

buildSrc/src/main/groovy/airbyte-java-cdk.gradle

@@ -32,7 +32,7 @@ class AirbyteJavaCdkPlugin implements Plugin<Project> {
         @TaskAction
         public void disableLocalCdkRefs() {
             // Step through the project tree and set useLocalCdk to false on all connectors
-            getProject().fileTree(dir: '.', include: '**/build.gradle').forEach(file -> {
+            getProject().rootProject.fileTree(dir: '.', include: '**/build.gradle').forEach(file -> {
                 String content = file.getText()
                 if (content.contains("useLocalCdk = true")) {
                     content = content.replace("useLocalCdk = true", "useLocalCdk = false")
@@ -48,7 +48,7 @@ class AirbyteJavaCdkPlugin implements Plugin<Project> {
         public void assertNotUsingLocalCdk() {
             List<String> foundPaths = new ArrayList<>()
 
-            for (File file : getProject().fileTree(dir: '.', include: '**/build.gradle')) {
+            for (File file : getProject().rootProject.fileTree(dir: '.', include: '**/build.gradle')) {
                 String content = file.getText()
                 if (content.contains("useLocalCdk = true")) {
                     System.err.println("Found usage of 'useLocalCdk = true' in " + file.getPath())