[MAYA-123816] testUsdExportRenderLayerMode with PR 2204

`testUsdExportRenderLayerMode`'s `testModelingVariantModeWithParentScope` test is failing because it's now creating a circular reference. `ConvertDagToUsdPath` logic has changed, causing a different return value that creates this circular dependency. There are more details in comments I added here:
https://github.com/Autodesk/maya-usd/commit/a4b8adaac3c1f1250d31c934f5173bc7932b9a73

This test is skipped when I run the test suite from our maya-usd open source tree because `USD render layer functionality can only be tested with Maya set to legacy render layer mode.` It was enabled in our internal tree, however, which is how I noticed this problem.

I've disabled our test internally for now, but I'm concerned this change may have had unintended consequences outside of this test case.

Steps to reproduce the behavior:
1. Configure your environment so `testUsdExportRenderLayerMode` is not skipped
2. Run tests with latest
3. Observe errors with UsdStage composition due to circular dependency

**Expected behavior**
Test passes

**Specs (if applicable):**
- Linux 64bit
- Maya 2022
- Maya USD commit SHA [dev at 9bdb040]
- Pixar USD commit SHA [dev at 5e2d09e]