Say YJIT is disabled by default in ruby --help

ruby.c

@@ -340,7 +340,7 @@ usage(const char *name, int help, int highlight, int columns)
 	M("rubyopt", "",        "RUBYOPT environment variable (default: enabled)"),
 	M("frozen-string-literal", "", "freeze all string literals (default: disabled)"),
         M("jit", "",            "JIT compiler (default: disabled)"),
-        M("yjit", "",           "in-process JIT compiler (default: enabled)"),
+        M("yjit", "",           "in-process JIT compiler (default: disabled)"),
     };
     static const struct message warn_categories[] = {
         M("deprecated", "",       "deprecated features"),