[QNN EP] Properly skip HTP test on x64 (#16500)
### Description
Fixes a typo that prevents skipping a test that targets the QNN HTP
backend on Windows x64.
### Motivation and Context
- Windows x64 machines cannot load/run the QNN HTP backend. Therefore,
we need to skip such tests on Windows x64.
- Fixes the QNN_Nuget_Windows pipeline.
