[NV TRT RTX EP] Add dimension override for TopK model in TestSessionOutputs unittest (#26975)
### Description
<!-- Describe your changes. -->
- Added dimension override in topk_and_multiple_graph_outputs model to
match K value
### Motivation and Context
<!-- - Why is this change required? What problem does it solve?
- If it fixes an open issue, please link to the issue here. -->
- topk_and_multiple_graph_outputs model in TestSessionOutputs unit test
was failing due to shape constraints: TopK: length of reduction axis (N)
is smaller than K (300) Condition '==' violated: 0 != 1