Update build.yml to fix the python version 3.8 for now

[NadeemYaseen]

Motivate of the pull request

• [ x] To address an existing issue. If so, please provide a link to the issue:
• Breaking new feature. If so, please describe details in the description part.

Describe the technical details

CI is broken due to change in GitHub action runner version so fixing it to make it compatible with our current setup

What is currently done? (Provide issue link if applicable)

What does this pull request change?

Which part of the code base require a change

• Build compatibility
• Documentation
• Regression tests
• [x ] Continous Integration (CI) scripts

Impact of the pull request

• Require a change on Quality of Results (QoR)
• Break back-compatibility. If so, please list who may be influenced.

[NadeemYaseen]

The actual error was to add these lines in patched VPR CMake.
Again we fell into the same trap, Xifin brought in large changes from the VPR submodule and our copying did not go well.
It is fixed PR #894