[kernel] Fix position ids in rope

[ByronHsu]

Motivation

There was an error. Not sure why the CI did not catch it.

Modifications

Checklist

• Format your code according to the Code Formatting with Pre-Commit.
• Add unit tests as outlined in the Running Unit Tests.
• Update documentation / docstrings / example tutorials as needed, according to Writing Documentation.
• Provide throughput / latency benchmark results and accuracy evaluation results as needed, according to Benchmark and Profiling.

[ByronHsu]

I see why. The command to run rope test should be pytest ... but we were using python ...