highlights(cpp): make "::" @punctuation.delimiter

Fixes #2902

queries/cpp/highlights.scm

@@ -174,10 +174,9 @@
  ;"xor_eq"
 ] @keyword.operator
 
-[
-  "<=>"
-  "::"
-] @operator
+"<=>" @operator
+
+"::" @punctuation.delimiter
 
 (attribute_declaration) @attribute
 

tests/query/highlights/cpp/test.cpp

@@ -10,6 +10,7 @@ auto main( int argc, char** argv ) -> int
       //                  ^ operator
 {
     std::cout << "Hello world!" << std::endl;
+    //  ^ punctuation.delimiter
     
     return EXIT_SUCCESS;
     // ^ keyword.return