Use versioned python3 command in scripts

[sbomer]

We would like to establish a simplified and generalized pattern for defining helix container images in our infrastructure, and reduce the number of workarounds required to satisfy specific test scenarios, such as https://github.com/dotnet/dotnet-buildtools-prereqs-docker/blob/e2ac99efb806885c8c253fa80aa65ca98e4ac3bb/src/almalinux/8/helix/amd64/Dockerfile#L22-L23.

To this end, aspnetcore should replace uses of unversioned python with the specific versioned executable (python3 unless there are python2 uses not covered by the test runs that I switched over to this image in #47970). This is in line with the best practice advice in https://developers.redhat.com/blog/2018/08/13/install-python3-rhel#python-tips.

cc @richlander

[richlander]

We're in the process of updating our helix Dockerfiles for .NET 8. We are revisiting all the patterns, particularly the anti-patterns.

Thanks for contacting us.

We're moving this issue to the .NET 8 Planning milestone for future evaluation / consideration. We would like to keep this around to collect more feedback, which can help us with prioritizing this work. We will re-evaluate this issue, during our next planning meeting(s).
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