Cmake error in DumuxTestMacros

Seems like !2408 (merged) introduces some cmake bug. With cmake 3.16 I get

CMake Error at dumux/cmake/modules/DumuxTestMacros.cmake:260 (file):
  Syntax error in cmake code at

    dumux/cmake/modules/DumuxTestMacros.cmake:261

  when parsing string

    \{\n  \"name\": \"${ADDTEST_NAME}\",\n  \"target\": \"${ADDTEST_TARGET}\"\n\}\n

  Invalid escape sequence \{