[spec-gen-sdk-runner] Remove dependency from unit tests to specification/contosowidgetmanager

[mikeharder]

The unit tests currently depend on specification/contosowidgetmanager, which is undesirable for a few reasons:

1. You need to clone this folder to run the tests. The tool isn't self-contained.
   

   azure-rest-api-specs/.github/workflows/spec-gen-sdk-runner-test.yaml

   Lines 30 to 32 in 8a01684

   	sparse-checkout-paths: |
   	specification/common-types
   	specification/contosowidgetmanager

2. Changes to the sample could break your tests. These should be decoupled.
3. Your tests fail in RPSaaSMaster, since this branch doesn't have the contoso data-plane. (example: https://github.com/Azure/azure-rest-api-specs-pr/actions/runs/13711484022)

Please update your tests to use a sample spec under your own test folder. This could even be a copy of contoso if you want.
Example:

https://github.com/Azure/azure-rest-api-specs/tree/main/eng/tools/typespec-requirement/test/specification