cmake: don't use reserved target name 'test'

CMake up to 3.10 always reserves this name

Fixes #6257
Closes #6258

tests/CMakeLists.txt

@@ -41,7 +41,6 @@ function(add_runtests targetname test_flags)
   )
 endfunction()
 
-add_runtests(test           "")
 add_runtests(test-quiet     "-a -s")
 add_runtests(test-am        "-a -am")
 add_runtests(test-full      "-a -p -r")