CMake: Fix build with SERVER=OFF and DOWNLOAD_GTEST=ON

Author: Kaffeine

CMakeLists.txt

@@ -2958,7 +2958,7 @@ add_custom_command(OUTPUT ${PROJECT_BINARY_DIR}/src/game/generated/checksum.cpp
 # TESTS
 ########################################################################
 
-if(GTEST_FOUND OR DOWNLOAD_GTEST)
+if((GTEST_FOUND OR DOWNLOAD_GTEST) AND SERVER)
   set_src(TESTS GLOB src/test
     aio.cpp
     bezier.cpp