Change some of status messages based on RFC 9110 (#1740)

httplib.h

@@ -1807,7 +1807,7 @@ inline const char *status_message(int status) {
   case 207: return "Multi-Status";
   case 208: return "Already Reported";
   case 226: return "IM Used";
-  case 300: return "Multiple Choice";
+  case 300: return "Multiple Choices";
   case 301: return "Moved Permanently";
   case 302: return "Found";
   case 303: return "See Other";
@@ -1836,7 +1836,7 @@ inline const char *status_message(int status) {
   case 417: return "Expectation Failed";
   case 418: return "I'm a teapot";
   case 421: return "Misdirected Request";
-  case 422: return "Unprocessable Entity";
+  case 422: return "Unprocessable Content";
   case 423: return "Locked";
   case 424: return "Failed Dependency";
   case 425: return "Too Early";