testing/openttd: build is broken

Fcaed when rebuilding the package for new icu !24901 (comment 177960)

-- Found Freetype: /usr/lib/libfreetype.so (found version "2.11.0") 
FATAL_ERROR,SDL2::SDL2 doesn't seem to contain any kind of lib to link against in IMPORTED_IMPLIB* or IMPORTED_LOCATION*
CMake Error at /usr/lib/cmake/SDL2/SDL2Config.cmake:94 (get_filename_component):
  get_filename_component called with incorrect number of arguments
Call Stack (most recent call first):
  CMakeLists.txt:132 (find_package)


-- Configuring incomplete, errors occurred!
See also "/mnt/testing/openttd/src/openttd-1.11.2/build/CMakeFiles/CMakeOutput.log".
>>> ERROR: openttd: build failed