vm_args.c: rephrase the warning message of keyword argument separation

(old)
test.rb:4: warning: The last argument is used as the keyword parameter
test.rb:1: warning: for `foo' defined here; maybe ** should be added to the call?

(new)
test.rb:4: warning: The last argument is used as keyword parameters; maybe ** should be added to the call
test.rb:1: warning: The called method `foo' is defined here

1 files changed, 1 insertions, 1 deletions

diff --git a/test/ruby/test_struct.rb b/test/ruby/test_struct.rb
index 9438160a6f..6f31b334b1 100644
--- a/test/ruby/test_struct.rb
+++ b/test/ruby/test_struct.rb
@@ -115,7 +115,7 @@ module TestStruct
     assert_equal "#{@Struct}::KeywordInitTrue(keyword_init: true)", @Struct::KeywordInitTrue.inspect
     # eval is needed to prevent the warning duplication filter
     k = eval("Class.new(@Struct::KeywordInitFalse) {def initialize(**) end}")
-    assert_warn(/The last argument is used as the keyword parameter/) {k.new(a: 1, b: 2)}
+    assert_warn(/The last argument is used as keyword parameters/) {k.new(a: 1, b: 2)}
     k = Class.new(@Struct::KeywordInitTrue) {def initialize(**) end}
     assert_warn('') {k.new(a: 1, b: 2)}