fix: minor CMake warning fix for unused variable (#3718)

tools/FindCatch.cmake

@@ -9,6 +9,8 @@
 #  CATCH_INCLUDE_DIR      - path to catch.hpp
 #  CATCH_INCLUDE_DIR      - path to catch.hpp
 #  CATCH_VERSION          - version number
 #  CATCH_VERSION          - version number
 
 
+option(DOWNLOAD_CATCH "Download catch2 if not found")
+
 if(NOT Catch_FIND_VERSION)
 if(NOT Catch_FIND_VERSION)
   message(FATAL_ERROR "A version number must be specified.")
   message(FATAL_ERROR "A version number must be specified.")
 elseif(Catch_FIND_REQUIRED)
 elseif(Catch_FIND_REQUIRED)