Don't set the Python path in Ubuntu jobs.

Signed-off-by: David Calavera <[email protected]>

Author: calavera

.appveyor.yml

@@ -16,28 +16,24 @@ environment:
       LINE_COVERAGE: "91"
       NEW_FLAKE8: 0
       JAVA_HOME: "C:\\Program Files\\Java\\jdk11"
-      CARGO_ZIGBUILD_PYTHON_PATH: "C:\\Python36-x64\\python.exe"
     - PYTHON: "C:\\Python37-x64"
       PYTHON_VERSION: "3.7"
       PYTHON_ARCH: "64"
       LINE_COVERAGE: "91"
       NEW_FLAKE8: 0
       JAVA_HOME: "C:\\Program Files\\Java\\jdk11"
-      CARGO_ZIGBUILD_PYTHON_PATH: "C:\\Python37-x64\\python.exe"
     - PYTHON: "C:\\Python38-x64"
       PYTHON_VERSION: "3.8"
       PYTHON_ARCH: "64"
       LINE_COVERAGE: "72"
       NEW_FLAKE8: 1
       JAVA_HOME: "C:\\Program Files\\Java\\jdk11"
-      CARGO_ZIGBUILD_PYTHON_PATH: "C:\\Python38-x64\\python.exe"
     - PYTHON: "C:\\Python39-x64"
       PYTHON_VERSION: "3.9"
       PYTHON_ARCH: "64"
       LINE_COVERAGE: "72"
       NEW_FLAKE8: 1
       JAVA_HOME: "C:\\Program Files\\Java\\jdk11"
-      CARGO_ZIGBUILD_PYTHON_PATH: "C:\\Python39-x64\\python.exe"
 
 build: off
 
@@ -83,8 +79,9 @@ for:
       - ps: "&powershell -NoProfile -ExecutionPolicy unrestricted -Command \"[Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls12; &([scriptblock]::Create((Invoke-WebRequest -UseBasicParsing 'https://dot.net/v1/dotnet-install.ps1'))) -Version 6.0.200 -InstallDir 'C:\\Program Files\\dotnet\\'\""
 
       # install Zig to cross compile Rust functions
-      - "%CARGO_ZIGBUILD_PYTHON_PATH% -m pip install ziglang"
-      - "%CARGO_ZIGBUILD_PYTHON_PATH% -m ziglang version"
+      - ps: "$env:CARGO_ZIGBUILD_PYTHON_PATH = \"$env:PYTHON\\python.exe\""
+      - ps: "$env:CARGO_ZIGBUILD_PYTHON_PATH -m pip install ziglang"
+      - ps: "$env:CARGO_ZIGBUILD_PYTHON_PATH -m ziglang version"
 
       # install Rust
       - appveyor-retry appveyor DownloadFile https://win.rustup.rs/ -FileName rustup-init.exe