Corrected image for test:windows_cpp

.gitlab/ci/test.gitlab-ci.yml

@@ -31,6 +31,7 @@ test:windows_cpp:
   needs: ["build:windows_cpp"]
   tags:
     - windows
+  image: buildtools
   script:
     - cd build_cpp
     - ctest --output-junit ctest-results.xml --output-on-failure