Enabled page heap verification (#4186)

Enabled page heap verification

.appveyor.yml

@@ -85,6 +85,7 @@ build_script:
 test_script:
 - cd c:\pillow
 - '%PYTHON%\%PIP_DIR%\pip.exe install pytest pytest-cov'
+- c:\"Program Files (x86)"\"Windows Kits"\10\Debuggers\x86\gflags.exe /p /enable %PYTHON%\%EXECUTABLE%
 - '%PYTHON%\%EXECUTABLE% -m pytest -vx --cov PIL --cov-report term --cov-report xml Tests'
 #- '%PYTHON%\%EXECUTABLE% test-installed.py -v -s %TEST_OPTIONS%' TODO TEST_OPTIONS with pytest?
 

.github/workflows/test-windows.yml

@@ -339,6 +339,13 @@ jobs:
         %PYTHON%\python.exe selftest.py --installed
       shell: cmd
 
+    # failing with PyPy3
+    - name: Enable heap verification
+      if: "!contains(matrix.python-version, 'pypy')"
+      run: |
+        c:\"Program Files (x86)"\"Windows Kits"\10\Debuggers\x86\gflags.exe /p /enable %PYTHON%\python.exe
+      shell: cmd
+
     - name: Test Pillow
       run: |
         set PYTHON=%pythonLocation%