CI-windows.yml: also run tests in Windows Server (Core) Docker container #1197

Job	Run time
build (windows-2025, Release)	1m 0s
build (windows-2025, Debug)	46s
test-core (mcr.microsoft.com/windows/server:ltsc2025, Release)	7s
test-core (mcr.microsoft.com/windows/server:ltsc2025, Debug)	7s
test-core (mcr.microsoft.com/windows/servercore:ltsc2025, Debug)	6s
test-core (mcr.microsoft.com/windows/servercore:ltsc2025, Release)	5s
test-core (mcr.microsoft.com/windows/server:ltsc2025, Debug)	4s
test-core (mcr.microsoft.com/windows/server:ltsc2025, Release)	3s
test-core (mcr.microsoft.com/windows/servercore:ltsc2025, Release)	6s
test-core (mcr.microsoft.com/windows/servercore:ltsc2025, Debug)	7s
build (windows-2025, Debug)	46s
build (windows-2025, Release)	1m 0s
build (windows-2025, Debug)	1m 3s
build (windows-2025, Release)	1m 7s
test-core (mcr.microsoft.com/windows/servercore:ltsc2025, Release)	7s
test-core (mcr.microsoft.com/windows/server:ltsc2025, Release)	5s
test-core (mcr.microsoft.com/windows/server:ltsc2025, Debug)	6s
test-core (mcr.microsoft.com/windows/servercore:ltsc2025, Debug)	6s
	6m 51s

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