interpreter: Ignore summary() for is_build_only

It's not really that useful anyway, so not worth dealing with
subproject summary collisions between build and host.

mesonbuild/interpreter/interpreter.py

@@ -1386,6 +1386,8 @@ def message_impl(self, args):
     )
     def func_summary(self, node: mparser.BaseNode, args: T.Tuple[T.Union[str, T.Dict[str, T.Any]], T.Optional[T.Any]],
                      kwargs: 'kwtypes.Summary') -> None:
+        if self.coredata.is_build_only:
+            return
         if args[1] is None:
             if not isinstance(args[0], dict):
                 raise InterpreterException('Summary first argument must be dictionary.')