Fix AppVeyor CI builds

.appveyor.yml

@@ -15,11 +15,16 @@ install:
   - findstr /V tput pytest.ini > pytest.ini.tmp
   - del pytest.ini
   - ren pytest.ini.tmp pytest.ini
-  # Add Make and Python to the PATH
+  # Add Make to the PATH
   - copy C:\MinGW\bin\mingw32-make.exe C:\MinGW\bin\make.exe
   - set PATH=%PATH%;C:\MinGW\bin
+  # Add Python to the PATH
   - set PATH=C:\Python%PYTHON_MAJOR%%PYTHON_MINOR%;%PATH%
   - set PATH=C:\Python%PYTHON_MAJOR%%PYTHON_MINOR%\Scripts;%PATH%
+  # Add Rust to the PATH
+  - appveyor DownloadFile https://win.rustup.rs/ -FileName rustup-init.exe
+  - rustup-init -yv --default-toolchain %channel% --default-host %target%
+  - set PATH=%PATH%;%USERPROFILE%\.cargo\bin
   # Install system dependencies
   - curl -sSL https://install.python-poetry.org | python -
   - set PATH=%USERPROFILE%\AppData\Roaming\Python\Scripts;%PATH%