Clinic test are skipped on Windows

[erlend-aasland]

test_clinic is skipped on Windows. This is a regression introduced by gh-96178.

• The Modules/_testclinic.c helper extension module is not included in the Windows build
• test.support.import_helper.import_module("_testclinic") fails and skips the whole test, since _testclinic is not found

Linked PRs

• gh-104629: Don't skip test_clinic if _testclinic is missing #104630
• [3.11] gh-104629: Don't skip test_clinic if _testclinic is missing (GH-104630) #104632
• gh-104629: Build _testclinic extension module on Windows #104723
• [3.12] gh-104629: Build _testclinic extension module on Windows (GH-104723) #107393

[erlend-aasland]

I'll leave the Windows specific part to someone with a Windows dev environment set up; I'm not comfortable doing the needed build changes in PCbuild/.

cc. @python/windows-team