🩹 Use #pragma once in pins files

Marlin/src/pins/ramps/pins_K8600.h

@@ -19,6 +19,7 @@
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  *
  */
+#pragma once
 
 /**
  * VERTEX NANO Arduino Mega with RAMPS EFB v1.4 pin assignments.

Marlin/src/pins/ramps/pins_TT_OSCAR.h

@@ -19,6 +19,7 @@
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  *
  */
+#pragma once
 
 #include "env_validate.h"