Optimize G-code flag parameters (#21849)

Marlin/src/gcode/sd/M27.cpp

@@ -33,7 +33,7 @@
  *      OR, with 'C' get the current filename.
  */
 void GcodeSuite::M27() {
-  if (parser.seen('C')) {
+  if (parser.seen_test('C')) {
     SERIAL_ECHOPGM("Current file: ");
     card.printSelectedFilename();
     return;

Marlin/src/gcode/sd/M808.cpp

@@ -44,7 +44,7 @@ void GcodeSuite::M808() {
   // Allowed to go into the queue for logging purposes.
 
   // M808 K sent from the host to cancel all loops
-  if (parser.seen('K')) repeat.cancel();
+  if (parser.seen_test('K')) repeat.cancel();
 
 }