Prefer using a binary upstream to building locally

Otherwise older python's fail trying to build pygame for the
test-suite

appveyor.yml

@@ -10,6 +10,7 @@ environment:
     # a later point release.
     # See: http://www.appveyor.com/docs/installed-software#python
 
+    # The tweak builds on the image where Python3.9 compatible compiler is available
     - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2019
       PYTHON: "C:\\Python39"
       PYTHON_VERSION: "3.9.0"
@@ -20,6 +21,8 @@ environment:
       PYTHON_VERSION: "3.9.0"
       PYTHON_ARCH: "64"
 
+    # Older Python's that can be built with the default windows images...
+
     - PYTHON: "C:\\Python36"
       PYTHON_VERSION: "3.6.4"
       PYTHON_ARCH: "32"
@@ -85,7 +88,7 @@ init:
 
 install:
   - "powershell appveyor\\install.ps1"
-  - "%CMD_IN_ENV% %PYTHON%\\python.exe -m pip install pygame pytest numpy"
+  - "%CMD_IN_ENV% %PYTHON%\\python.exe -m pip install --prefer-binary pygame pytest numpy"
   - "%CMD_IN_ENV% %PYTHON%\\python.exe setup.py install"
   - cd accelerate
   - "%CMD_IN_ENV% %PYTHON%\\python.exe setup.py install"