Enable heap verification without gflags

[radarhere]

GitHub Actions have started failing in main for Windows at the "Enable page verification" step.

Pillow/.github/workflows/test-windows.yml

Lines 140 to 143 in 4638c4f

	# 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 $env:pythonLocation\\python.exe"

The error is

The term 'C:\Program Files (x86)\Windows Kits\10\Debuggers\x86\gflags.exe' is not recognized as a name of a cmdlet, function, script file, or executable program.

The problem started at the same time that the jobs switched from windows-2019 to windows-2022. It looks like windows-2022 does not have gflags.exe.

Taking advice from "How to enable PageHeap in Windows registry without having access to gflags.exe", this PR fixes the problem.

While this could now be used on PyPy, it takes an hour to do so, so I have continued to skip heap verification on PyPy.

[radarhere]

Unrelated, I've added a commit to fix the currently failing MinGW builds.