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

.github/workflows/action.yml

@@ -173,7 +173,7 @@ jobs:
           CC: ${{ matrix.cc }}
           CXX: ${{ matrix.cxx }}
         working-directory: cmake-build
-        run: ctest -V
+        run: ctest -V -C Debug
 
       - name: Upload logs on failure
         uses: actions/upload-artifact@v2