github actions: Add dummy ctest config switch.

This is required on windows, but not on other platforms.
It needs to be the default `Debug` target, rather than
`Release` to match CMAKE_BUILD_TYPE, for the $TARGET_FILE
mapping to produce the correct path.

See https://gitlab.kitware.com/cmake/cmake/-/issues/20283
3 jobs for master in 35 minutes and 32 seconds (queued for 2 seconds)
Status Name Job ID Coverage
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passed autotools #11913
docker

00:22:22

passed cmake #11914
docker

00:14:26

passed makefile #11915
docker

00:21:03