Fix python arch on the windows arm64 CI
https://ci-external.swift.org/job/swift-main-windows-toolchain-arm64/777/consoleText
```
Error: Program 'python.exe' failed to run: The specified executable is not a valid application for this OS platform.At C:\Users\swift-ci\jenkins\workspace\swift-main-windows-toolchain-arm64\swift\utils\build.ps1:545 char:7
+ & $Executable @Args | Out-Null
+ ~~~~~~~~~~~~~~~~~~~.
```
