Fail gracefully instead of crashing on visible(), siblings() for cquery

PiperOrigin-RevId: 307436837
diff --git a/src/main/java/com/google/devtools/build/lib/query2/PostAnalysisQueryEnvironment.java b/src/main/java/com/google/devtools/build/lib/query2/PostAnalysisQueryEnvironment.java
index d670db1..aedd243 100644
--- a/src/main/java/com/google/devtools/build/lib/query2/PostAnalysisQueryEnvironment.java
+++ b/src/main/java/com/google/devtools/build/lib/query2/PostAnalysisQueryEnvironment.java
@@ -482,8 +482,8 @@
   }
 
   @Override
-  public Collection<T> getSiblingTargetsInPackage(T target) {
-    throw new UnsupportedOperationException("siblings() not supported");
+  public Collection<T> getSiblingTargetsInPackage(T target) throws QueryException {
+    throw new QueryException("siblings() not supported for post analysis queries");
   }
 
   @Override