fix(frontend/builder): Fix moved blocks disappearing on no-op save (#10927)

- Resolves #10926

### Changes 🏗️

- Fix save no-op if graph has no changes

### Checklist 📋

#### For code changes:
- [x] I have clearly listed my changes in the PR description
- [x] I have made a test plan
- [x] I have tested my changes according to the test plan:
- [x] Saving a graph after only moving nodes doesn't make those nodes
disappear

autogpt_platform/frontend/src/hooks/useAgentGraph.tsx

@@ -641,7 +641,7 @@ export default function useAgentGraph(
     let newSavedAgent: Graph;
     if (savedAgent && graphsEquivalent(savedAgent, payload)) {
       console.warn("No need to save: Graph is the same as version on server");
-      newSavedAgent = savedAgent;
+      return savedAgent;
     } else {
       console.debug(
         "Saving new Graph version; old vs new:",