Pin test python version to pyoxidizer python version

[SteinRobert]

What happened?

Different versions of Python are used in testing and the build executable.

What did you expect to happen?

Same versions should be used.

How can we reproduce it (as minimally and precisely as possible)?

What Kubernetes setup are you working with?

$ kubectl version
# paste output here

OS version

# On Linux:
$ cat /etc/os-release
# paste output here
$ uname -a
# paste output here

# On Windows:
C:\> wmic os get Caption, Version, BuildNumber, OSArchitecture
# paste output here

Anything else we need to know?

No response