win32: simplify the test matrix.

python3.5 is long EOL'd.

appveyor.yml

@@ -74,11 +74,13 @@ environment:
       PYTHON_ARCH: "32"
       PYTHON_VERSION: "3.5.x"
       PYTHON_EXE: python
+      GWHEEL_ONLY: true
 
     - PYTHON: "C:\\Python35-x64"
       PYTHON_ARCH: "64"
       PYTHON_VERSION: "3.5.x"
       PYTHON_EXE: python
+      GWHEEL_ONLY: true
 
     - PYTHON: "C:\\Python37"
       PYTHON_ARCH: "32"
@@ -94,6 +96,7 @@ environment:
       PYTHON_ARCH: "32"
       PYTHON_VERSION: "3.8.x"
       PYTHON_EXE: python
+      GWHEEL_ONLY: true
 
     - PYTHON: "C:\\Python38-x64"
       PYTHON_ARCH: "64"
@@ -104,11 +107,13 @@ environment:
       PYTHON_ARCH: "32"
       PYTHON_VERSION: "3.6.x"
       PYTHON_EXE: python
+      GWHEEL_ONLY: true
 
     - PYTHON: "C:\\Python36-x64"
       PYTHON_ARCH: "64"
       PYTHON_VERSION: "3.6.x"
       PYTHON_EXE: python
+      GWHEEL_ONLY: true
 
 cache:
   - "%TMP%\\py\\"
@@ -177,7 +182,7 @@ build_script:
 
 test_script:
   - "%CMD_IN_ENV% python -c \"import faulthandler; assert faulthandler.is_enabled()\""
-  - "%CMD_IN_ENV% python -m zope.testrunner --test-path=src -vvv"
+  -  if not "%GWHEEL_ONLY%"=="true" %PYEXE% -m zope.testrunner --test-path=src -vvv
 # XXX: Doctest disabled pending sphinx release for 3.10; see tests.yml.
 #  - "%CMD_IN_ENV% python -m sphinx -b doctest -d docs/_build/doctrees docs docs/_build/doctest"