Fix CI failures of the unity test build

- keep JSON_DISABLE_ENUM_SERIALIZATION and
  JSON_DISABLE_TUPLE_REFERENCE_CONVERSION defined with
  JSON_TEST_KEEP_MACROS, so that every file of a batch sees them, not only
  the first one
- mark JSON_TESTS_PRIVATE in the generated batch file as used, as GCC and
  Clang report an unused definition when the first file defines it again
  (-Wunused-macros)
- suppress bugprone-suspicious-include for the #include-d .cpp files
- avoid local json aliases and variables that hide a global json of
  another file in the same batch (MSVC C4459)

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

single_include/nlohmann/json.hpp

@@ -35304,8 +35304,6 @@ struct formatter<nlohmann::NLOHMANN_BASIC_JSON_TPL, char> // NOLINT(cert-dcl58-c
 #undef NLOHMANN_CAN_CALL_STD_FUNC_IMPL
 #undef JSON_INLINE_VARIABLE
 #undef JSON_NO_UNIQUE_ADDRESS
-#undef JSON_DISABLE_ENUM_SERIALIZATION
-#undef JSON_DISABLE_TUPLE_REFERENCE_CONVERSION
 
 #ifndef JSON_TEST_KEEP_MACROS
     #undef JSON_CATCH
@@ -35330,6 +35328,8 @@ struct formatter<nlohmann::NLOHMANN_BASIC_JSON_TPL, char> // NOLINT(cert-dcl58-c
     #undef JSON_STRICT_BINARY_UTF8
     #undef JSON_DELETE_DEPRECATED_FUNCTIONS
     #undef JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
+    #undef JSON_DISABLE_ENUM_SERIALIZATION
+    #undef JSON_DISABLE_TUPLE_REFERENCE_CONVERSION
 #endif
 
 // #include <nlohmann/thirdparty/hedley/hedley_undef.hpp>