cmake: fix "make check"

CMake 3.30 was giving error:

 CMake Error: Unknown argument: -C

probably because CMAKE_BUILD_TYPE was not set, which made
$<CONFIGURATION> an empty string. Try adding quotes.
Do we need -C at all?

Since $<CONFIGURATION> is deprecated, use $<CONFIG>.

CMakeLists.txt

@@ -413,7 +413,7 @@ add_custom_target(print-version
   COMMENT "gemmi --version"
 )
 
-add_custom_target(check COMMAND ${CMAKE_CTEST_COMMAND} -C $<CONFIGURATION>)
+add_custom_target(check COMMAND ${CMAKE_CTEST_COMMAND} -C \"$<CONFIG>\")
 add_test(NAME cpptest COMMAND cpptest)
 
 add_dependencies(check