onnxruntime

Set pythonInterpreter in set-python-manylinux-variables-step.yml (#19105)

### Description
Set pythonInterpreter in set-python-manylinux-variables-step.yml. To fix
a build error:

```
Starting: Set Python manylinux variables
==============================================================================
Task         : Python script
Description  : Run a Python file or inline script
Version      : 0.231.1
Author       : Microsoft Corporation
Help         : https://docs.microsoft.com/azure/devops/pipelines/tasks/utility/python-script
==============================================================================
##[error]Parameter 'toolPath' cannot be null or empty.
Finishing: Set Python manylinux variables
```
The error was because today I deleted a bunch of software from the VM
image. The task might fail if no Python versions are found in
$(Agent.ToolsDirectory).