package: build tests also in MinGW Jenkins configuration.

We want to test at least that they build successfully.

package/ci/jenkins-mingw32.xml

@@ -79,6 +79,7 @@ cmake .. \
     -DCMAKE_TOOLCHAIN_FILE=../toolchains/archlinux/basic-mingw32.cmake \
     -DCMAKE_FIND_ROOT_PATH=${JENKINS_HOME}/filesystem/mingw32-${libraries} \
     -DCMAKE_INSTALL_PREFIX=${JENKINS_HOME}/filesystem/mingw32-${libraries}-${compatibility} \
+    -DBUILD_TESTS=ON \
     -DBUILD_DEPRECATED=${deprecated_build_flag} \
     ${static_build_flag} \
     -DWITH_AUDIO=ON \